Chapter 9: Sleep, Stress and the Tired Brain

When Good Habits Fall Apart

Abdi is forty-one and leads a team of twelve in a company that provides customer support for internet services. For most of last year, his habits were in good shape. He walked to work, ate a healthy lunch, went to bed at a reasonable time, read with his children in the evenings and kept his temper even with difficult customers. He felt proud of the routines he had built.

Then, in the autumn, several things happened at once. His company introduced a new system that caused many problems, and his team was overwhelmed with complaints. His youngest child started waking several times a night. Abdi began sleeping only five or six hours, often broken. Within a few weeks, his habits started to fall apart. He took the bus instead of walking, because he was too tired. He ate snacks from the vending machine instead of his packed lunch. He stayed up late, scrolling on his phone, even though he was exhausted. He snapped at his team and, worse, at his children.

Abdi felt ashamed. He had worked so hard to build good habits, and now they were disappearing. He felt that he had lost his discipline and that he was becoming a worse person.

What Abdi did not see at the time was how predictable his collapse had been. He had built his routines during a calm, well-rested period. They depended on a brain that had the energy to make deliberate choices. When the energy disappeared, the routines that were still new and still needed effort were the first to go, while older, easier habits, like reaching for his phone, filled the gap. He was not becoming a worse person. His brain was simply doing what tired brains do. He tried to force himself back into his routines, but every morning he woke up exhausted, and by evening he had no energy left for anything but the sofa and his phone.

One evening, his sister, who works as a nurse, came to visit. She looked at him and said, "You are not lazy. You are exhausted. Your brain is worn out. It is very hard for anyone to keep good habits on five hours of broken sleep." She suggested that, before worrying about his other habits, he focus on two things: getting more sleep, and finding ways to reduce the stress that was keeping him awake.

Abdi's experience shows something that many people discover the hard way: sleep and stress have a powerful effect on our habits. This chapter looks at what brain science says about how tiredness and stress change the way we behave, and why protecting sleep and managing stress can be among the most important habits of all.

The Tired Brain

Sleep is not simply a period of rest. While we sleep, the brain carries out many important processes, and research over many decades has shown that losing sleep affects how the brain works in the day. It is well established that sleep loss impairs attention, slows reactions and makes it harder to think clearly and make good decisions. It also tends to affect mood, making people more irritable, more easily upset and less able to manage their emotions.

Some of these effects seem to involve the parts of the brain we met in Chapter 1. Studies using brain scans have suggested that, after sleep loss, the prefrontal cortex, the area involved in planning, deliberate control and weighing long-term goals, works less effectively, while areas involved in emotional reactions may respond more strongly. This is a simplified picture, and scientists are still exploring the details. But it fits everyday experience: when we are tired, we find it harder to think ahead, harder to resist temptations and easier to react strongly.

For habits, this has an important consequence. If the deliberate system is weakened by tiredness, we rely more on the automatic system. Whatever habits we already have tend to take over. If our strongest habits are helpful, tiredness may not disrupt them much. But if we are in the middle of building new habits, which still need deliberate effort, or resisting old ones, tiredness makes this much harder. This is part of why Abdi's new, carefully built routines collapsed, while older habits, such as reaching for his phone, became stronger.

Research has also looked at how sleep loss affects specific choices. Some studies have suggested that people who are short of sleep tend to choose more high-energy, sugary or fatty foods and feel stronger urges for them. Others have found that tired people are more likely to put off tasks and less likely to exercise. These findings vary between studies, but the general direction is consistent: tiredness tends to push behaviour toward the easy, the immediate and the familiar.

There is also a positive side. Research suggests that sleep helps the brain consolidate what it has learned during the day, including new skills. Some studies have found that people perform better at newly learned movement tasks after a night of sleep than after the same amount of time awake. Sleep may therefore help new habits, as well as protecting the deliberate effort that new habits need. In this sense, good sleep is not only a habit in itself. It supports almost every other habit we try to build.

Stress and the Retreat to Routine

Stress affects habits in a related way. Studies in animals and in people have suggested that under stress, behaviour tends to shift away from deliberate, goal-directed control and toward habit. In experiments where people learned a task and were then put under stress, for example by being asked to give a speech or to hold their hand in cold water, they were more likely to continue responding in habitual ways, even when the situation had changed and a different response would have been better (this summarizes a line of research that is still developing).

Researchers suggest that this may make sense from the brain's point of view. When we are under threat or pressure, quick, familiar responses may be safer than slow, careful thinking. Habits are fast and reliable. In a crisis, falling back on what we know may help us survive. But in modern life, where most stress comes from work, money, relationships and worry rather than from physical danger, this shift can lead us back to habits we were trying to change, such as eating for comfort, scrolling, smoking or snapping at people.

This finding helps explain a common experience: our resolutions often collapse during stressful periods. We may manage a new habit well for weeks, then a stressful event arrives, and we find ourselves back in old patterns. This is not because we suddenly became weak. It is partly because stress tips the balance in the brain toward the automatic system, and the automatic system runs our oldest and strongest habits.

The same finding also contains a hopeful message. If stress pushes us toward habits, then the habits we build during calm times will be the ones that carry us through stressful times. A person who has built a strong habit of a short walk each day, or of calling a friend when upset, may find that these habits continue even under stress, because they have become automatic. Building helpful habits in calm periods is like preparing a path that stress will push us onto.

Sleep and stress are also connected with each other. Stress often disturbs sleep, as it did for Abdi, and lack of sleep makes stress harder to manage, creating a cycle. Breaking this cycle, by protecting sleep and finding ways to reduce or manage stress, can help restore the conditions in which good habits can grow. It is worth saying, too, that both long-lasting sleep problems and heavy, ongoing stress can affect health, and that they are good reasons to talk with a doctor or another qualified professional.

Abdi Puts Sleep First

Following his sister's advice, Abdi decided to stop trying to rescue all his habits at once. Instead, he focused on sleep. He talked with his partner, and they agreed to take turns getting up with their youngest child at night, so that each of them had some nights of unbroken sleep. On his nights off, Abdi went to bed early and wore earplugs.

Abdi also looked at his own habits around sleep. He realized that his late-night scrolling, which had grown during the stressful period, was taking away the sleep he desperately needed and keeping his mind active. Using the ideas from earlier chapters, he moved his phone charger to the kitchen and put a book by his bed. He set a regular time for going to bed and tried to keep to it. He stopped drinking coffee after lunchtime, because he noticed that afternoon coffee made it harder to fall asleep.

At work, Abdi addressed some of the stress. He talked with his manager about the problems with the new system and asked for extra help for his team during the difficult period. He began taking a short walk at lunchtime, even when he felt too busy, because it helped him clear his head. He reminded himself that the crisis with the new system would not last forever.

Abdi also made a decision that felt strange to him at first. He stopped trying to keep all his good habits during the difficult weeks. Instead, he chose two to protect, sleep and the lunchtime walk, and let the others rest for a while. He told himself that he would rebuild the rest once things were calmer. This took away much of the guilt he had been feeling, and, oddly, made it easier to keep the two habits he had chosen.

Within a few weeks, Abdi was sleeping better, and his child had started sleeping through the night more often. As his sleep improved, he noticed that his other habits began to return, almost by themselves. He felt like walking to work again. He packed his lunch. He had the patience to read with his children. He did not have to force these habits back. They came back naturally once his brain was rested.

"I was trying to fix everything with willpower," Abdi says. "But it is very hard to make good choices on five hours of sleep. Once I fixed my sleep, everything else became possible again." Abdi's story shows that sleep is not just one habit among many. For many people, it is the foundation on which other habits rest.

Margarita in the Hard Months

Margarita is fifty and works as an administrator in a primary school. For the past six months, she has also been caring for her elderly mother, who has become frail and needs help with many daily tasks. Margarita visits her mother every evening after work and spends most weekends with her. She is exhausted and stressed, and she worries constantly about her mother's health.

Margarita has noticed that, during these months, she has fallen back into some old habits. She eats crisps and chocolate in the evenings, which she had stopped doing years ago. She has stopped going to her weekly choir practice. She often feels too tired to cook and eats ready meals. She feels guilty about all of this, which adds to her stress.

But Margarita has also noticed something interesting. One habit has survived: her early morning walk. For several years before her mother became ill, she had walked for twenty minutes every morning before work, along the same route, with her neighbour. This habit had become so automatic that it continued even in the hardest weeks. She found that the walk was the one part of her day that felt calm, and that it helped her face everything else.

When Margarita read about how stress pushes people toward their established habits, she understood her experience better. The old snacking habit had returned because stress had tipped her toward old automatic patterns. But the walking habit, which she had built carefully in calmer times, had also become automatic, so it had survived. She realized that she did not need to blame herself for the snacks. She needed to look after herself during a very hard time, and to protect the helpful habits she still had.

Margarita made a few small changes. She stopped keeping crisps in the house, so that the old habit had less to work with. She asked her brother to take over some of the weekend visits to their mother. And she found out about local services that could provide some support for her mother at home. She also talked with her doctor about how tired and stressed she felt, and found the conversation helpful. "I learned that the habits I build when life is calm are the ones that carry me when life is hard," she says. "So now I try to build them while I can." Caring for a family member is a heavy load, and carers deserve support too.

Sven and the Late Nights

Sven is twenty-two and studies engineering at a university. During exam periods, he stays up very late, sometimes all night, studying and drinking strong coffee and energy drinks. He believes that more hours of study mean better results. But he has noticed that, after these nights, he struggles to remember what he studied, makes careless mistakes in practice problems and feels irritable and low for days afterwards.

A tutor at his university, noticing how tired Sven looked, explained some of what research suggests about sleep and learning. Sleep, she said, seems to help the brain store and strengthen what it has learned during the day.

She also pointed out that the energy drinks and late coffee he relied on might be making the problem worse. Caffeine can stay active in the body for many hours, and for many people, drinking it late in the day makes it harder to fall asleep and to sleep deeply. Sven had been using caffeine to make up for lost sleep, and the caffeine had been helping to cause the loss. It was a cycle he had never noticed. Studying all night and then sleeping very little might mean that much of what Sven studied was not consolidated properly. And sleep loss would make it harder for him to think clearly in the exam itself.

Sven was sceptical, but he decided to try a different approach for one exam period. He studied in focused sessions during the day, took regular breaks and stopped studying by ten in the evening. He stopped drinking coffee after mid-afternoon. He aimed for seven to nine hours of sleep each night, the common general guide for adults, going to bed and getting up at roughly the same times. He also took short walks during his breaks, which helped him feel more alert.

To his surprise, Sven found that he remembered more of what he studied and made fewer careless mistakes. He felt calmer during the exam period and did not crash afterwards. His results were better than in previous exam periods. "I thought sleep was time I could not afford," he says. "Actually, it was the time when my brain was doing the most important work."

Sven's story reflects a common experience among students and workers who try to push through tiredness. Research on sleep and learning is still developing, and individual needs for sleep vary. But the general finding that sleep supports memory and clear thinking is well established, and many people find, like Sven, that protecting their sleep improves both their wellbeing and their results.

Practical Steps: Protecting the Foundations

The first step is to notice how sleep and stress affect your habits. Pay attention to how your behaviour changes on days after poor sleep, or during stressful periods. Which habits weaken? Which old habits return? This awareness can help you understand that these changes are not simply failures of discipline.

The second step is to make sleep a priority habit. If you are trying to change several habits, consider starting with sleep. Aim for regular times for going to bed and getting up, even at weekends if you can. Give yourself enough time in bed. As a general guide, many adults need around seven to nine hours, though needs vary between people.

The third step is to design your evening for sleep. Use the ideas from earlier chapters: move screens out of the bedroom, keep a book by the bed, create a short wind-down routine, such as dimming the lights and having a warm drink without caffeine. Notice whether caffeine late in the day affects your sleep, and adjust if it does.

The fourth step is to build helpful habits during calm times. Since stress tends to push us toward our established habits, use calmer periods to build habits that will help you when stress comes: a daily walk, a regular call with a friend, a simple way of relaxing. Like Margarita's morning walk, these habits can become a source of strength in hard times.

The fifth step is to reduce what you can of the stress. Some stress cannot be avoided. But some can be reduced: by asking for help, sharing responsibilities, talking with a manager, setting limits or finding practical support. Reducing stress where possible also helps protect sleep and habits.

The sixth step is to be gentle with yourself during hard periods. When you are exhausted or under heavy stress, do not expect to maintain every habit perfectly. Focus on a few essential ones, especially sleep, and let others wait until life is calmer. Recognizing that your brain is under strain, rather than blaming yourself, can make hard periods easier to bear.

Sleep Advice Does Not Fit Every Life

General advice about sleep, such as regular bedtimes and enough hours in bed, is helpful for many people, but it does not fit every life. Shift workers, new parents, carers and people with certain health conditions may not be able to follow it easily. If your circumstances make good sleep difficult, it may help to focus on what you can control, such as protecting the sleep opportunities you do have, and to seek advice about your particular situation.

For shift workers in particular, some practical ideas may help, though each person's situation is different. Keeping the bedroom as dark and quiet as possible during daytime sleep, using the same short wind-down routine before every sleep, whatever the time, and being careful with caffeine toward the end of a shift are often suggested. It may also help to talk with colleagues about what works for them, and to seek advice from a doctor or another qualified professional if tiredness is persistent.

It is also important to recognize when sleep problems are more than a matter of habit. If you have difficulty falling asleep or staying asleep most nights for weeks or months, if you feel very sleepy during the day despite spending enough time in bed, if you snore heavily or stop breathing at night, as a partner might notice, or if sleep problems are affecting your health or safety, please talk to a doctor or another qualified professional. Some sleep problems have causes that can be treated, and it is worth finding out.

Similarly, stress that is heavy, constant or overwhelming may need more than habit changes. If stress is affecting your health, your mood or your ability to cope, please talk to someone you trust and consider speaking with a doctor or another qualified professional. And if you ever feel that you might hurt yourself, or if you are in danger, contact a helpline or a medical facility right away, and in immediate danger call your local emergency number.

A Short Exercise: A Sleep and Habit Diary

This exercise helps you see how sleep and stress affect your habits. It takes a couple of minutes each day for two weeks.

Each morning, write down roughly how many hours you slept and how rested you feel, on a scale from one, very tired, to five, very rested. Each evening, write down your stress level for the day, from one, very calm, to five, very stressed, and note whether you kept up the habits you are working on or fell back into old ones. Keep it brief: a few words for each habit is enough.

After two weeks, look at your diary. Do you notice any patterns? On days after poor sleep, did your habits slip? On high-stress days, did old habits return? Were there any habits that held up even on hard days? Write down what you notice.

Based on what you have seen, choose one change to protect your sleep, such as a regular bedtime, a phone-free bedroom or no caffeine after lunch. Choose one change to reduce or manage stress, such as a daily walk, asking for help with one task or a short break during the day. Write them down and try them for the next two weeks.

Abdi did this exercise after his conversation with his sister. His diary showed that on every day after less than six hours of sleep, he skipped his walk, ate snacks for lunch and stayed up late on his phone. On the two days after good sleep, he kept almost all his habits. "It was so clear," he says. "My habits were not the problem. My sleep was."

Chapter Summary

Sleep loss is well known to impair attention, decision-making and emotional control, and brain studies suggest that it weakens the deliberate functions of the prefrontal cortex while emotional reactions may become stronger. When tired, people tend to rely more on automatic habits and to choose what is easy and immediate. Sleep also appears to help the brain consolidate learning. Studies in animals and people suggest that stress tends to shift behaviour toward habit, which helps explain why resolutions often collapse in stressful times, and why habits built in calm times can carry us through hard ones.

Abdi and his collapsing routines, Margarita in her hard months of caring, and Sven with his late nights before exams all found that protecting sleep and reducing stress where possible restored the conditions in which good habits could survive and grow. Sleep advice does not fit every life, and long-lasting sleep problems or heavy stress deserve a conversation with a doctor or another qualified professional.

In the next chapter, we will look at one of the most famous experiments in psychology, involving children and sweets, and at what it really tells us about self-control.