Explore each chapter to understand the effort, benefits and context.
This chapter counts energy and time: usable attention, reaction speed, errors, and how long it takes to return after an interruption. The figures are measured directly in experiments or observational cohorts, without conversion into lifespan or mortality. Most entries receive grade B; that reflects the evidence available in this field, not proof that the advice is wrong. Entry 20, about expectations when dealing with police, clinicians and counter staff, cites regulations rather than experiments and receives grade C. Entry 15, on pessimistic thoughts, and entry 23, on feeling that others demand perfection, cite mortality and suicide-risk outcomes. Those measures differ from the rest and should not be compared directly.
A notification can impair attention even if you do not look at or touch your phone, by an amount comparable to taking a call or texting. Even resisting a phone sitting on the desk can leave less mental capacity available. People most dependent on their phones showed the largest drop.
The least regular fifth of sleepers had body clocks about 2.5 hours later than the most regular fifth—effectively living with persistent jet lag. More regular students also had better grades.
Two weeks at six hours a night produced cognitive impairment comparable to two nights without sleep. People did not fully notice: self-rated sleepiness rose in the first few days and then leveled off, with six-hour and four-hour sleepers reporting similar tiredness. Feeling that six hours is enough can itself reflect poor awareness of sleep loss.
Taking 400 mg of caffeine six hours before bed shortened objectively measured sleep by over an hour, although sleep diaries did not detect the difference. The pooled estimate suggests finishing an ordinary 107 mg coffee at least 8.8 hours before bedtime; for an 11 p.m. bedtime, that is about 2 p.m.
During a two-week comparison in the same people, the week limited to three email checks daily brought significantly less stress without fewer messages received or answered. Unrestricted checking averaged 15.5 times daily at baseline.
Interruptions averaging 2.8 seconds doubled subsequent step errors; 4.4 seconds tripled them. In field observation, returning to an interrupted activity took about 25 minutes, with two other activities in between. Interrupted people worked faster but felt more stressed, frustrated and strained.
Switching tasks slows responses and increases errors. Frequent users of several media streams had not trained themselves to multitask better; they performed worse on switching tests.
Reading a light-emitting screen before bed delayed sleep by about 10 minutes, suppressed melatonin by 55%, shifted the body clock over 1.5 hours later and left people sleepier and slower to become alert the next morning.
In 2025, Chinese residents averaged 6.97 hours of nighttime sleep and fell asleep around 00:10. Bedtime phone or tablet use was associated with over twice the odds of insufficient sleep and 2.7 times the odds of daytime sleepiness. Merely having a device in the bedroom showed similar associations.
Rested people quickly learned to avoid risky choices in a laboratory task. After two sleepless nights, they repeatedly chose riskier options, especially at older ages. This study did not measure losing only a few hours, but important decisions can wait until morning.
A ten-minute nap improved alertness immediately, with some effects lasting two and a half hours. Five minutes did little. Twenty minutes took over half an hour to help. Thirty minutes initially produced grogginess and worse performance than not napping.
Increasing background noise from 39 to 51 decibels reduced word recall and made people more tired and less motivated. During breaks, a nature film with sound restored energy better than continued office noise.
Records from British munitions factories during World War I showed output rising proportionally up to 49 weekly hours. Beyond that, each additional hour produced less. Seventy hours produced almost the same output as 56; the extra 14 hours added virtually nothing.
Replaying an upsetting event is not necessarily problem-solving. It can deepen depression, reinforce negative thoughts, impair solutions and action, and exhaust the people willing to listen. When you notice the loop, do something that involves your hands.
In a 20-year twin study, each standard-deviation increase in pessimism was associated with about 13% higher overall mortality and 20% higher cardiovascular mortality. Higher optimism did not show a corresponding benefit. The concern is persistent pessimism, not failure to be upbeat enough.
In the cited study, harmful interactions had stronger and more consistent associations with well-being than supportive interactions. Removing a source of strain may matter more than adding another source of support.
Strong evidence is lacking. The claim that choices deplete a finite supply of willpower failed in two large, multi-laboratory replications involving roughly two and three thousand people. Defaults may still save minutes and indecision, without “conserving willpower.”
Reinterpreting an event or taking another perspective can reduce emotional intensity; perspective-taking performed better in the cited analysis. Suppressing the feeling did not help. People who retaliated also dwelled on the offender longer, while those who did not moved on sooner; people overestimated how satisfying revenge would feel.
Walking and jogging showed the strongest exercise effects on depression, followed by yoga and strength training, with larger effects at higher intensity. Light therapy helped seasonal depression strongly and nonseasonal depression too. Online self-help CBT courses worked; guidance helped more when symptoms were more severe. In China, call 12356 when you need psychological support.
These are people doing jobs governed by rules, paperwork, deadlines and oversight. Their manner does not reliably tell you whether your case will be handled or when. Obtain receipts, record deadlines and use review or complaint channels instead of trying to win personal agreement.
Comparing yourself online with people who seem better off is associated with worse mood and lower self-esteem. Deactivating Facebook for four weeks modestly improved well-being but reduced knowledge of current affairs. Limiting three platforms to ten minutes each daily reduced loneliness and depression after three weeks.
People wearing an embarrassing T-shirt expected nearly half the room to recognize its image; fewer than a quarter did. For a self-chosen flattering shirt, the estimate was six times the actual recognition rate. People also tend to underestimate how much conversation partners like them. Halving the feeling that “everyone remembers” may still leave an overestimate.
Feeling that others require perfection and will reject you for falling short is associated with more suicidal thoughts. Self-imposed perfectionism has a much weaker relationship, about one-third as strong. After accounting for initial suicidal thoughts, perceived external demands still predicted a small increase in later thoughts.
Activities that increase arousal, such as hitting a punching bag, breaking objects or going for a run to vent, did not reduce anger overall. Slow breathing, mindfulness and meditation did reduce anger and aggressive urges.
Expressive writing has a small average benefit in some analyses, but findings differ and two reviews found no significant effect. It costs little and can be tried, but should not replace care for serious emotional problems.