Don't make big decisions or send important messages late at night

Moderate value
Evidence B
Saves time
Free
Takes minutes
Some willpower

In plain words

When people are well rested, they quickly learn to avoid high-risk options. After two nights without sleep, they instead keep choosing high-risk ones, and the effect is stronger the older the person. How much a few hours of lost sleep matters has not been measured, but it is still better to put important decisions off until after you have slept.

Cost: Free. You just put things off until after you have slept.
What you get: 34 healthy people did the Iowa Gambling Task after 49.5 hours without sleep. This is an experiment that measures risky decision-making. When rested, they quickly learned to avoid high-risk options. After sleep loss, they chose more high-risk options instead. Older people were affected more. This was one experiment, and this is the only study.
Notes: The study looked at the extreme case of two nights in a row without sleep. What happens to an ordinary person who stays up until 2 a.m. has not been measured directly. The “don't send messages” half comes from the author's own experience (grade C); sending it the next day is not too late.
Evidence grade: B : Supported by research but without a precise number, or based on small or single studies.
Sources: Killgore, Balkin & Wesensten (2006). Impaired decision making following 49 h of sleep deprivation. Journal of Sleep Research. https://doi.org/10.1111/j.1365-2869.2006.00487.x

Translated from the Chinese original. Original book, section 3, tip 10. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer