Sleep is one of the most powerful foundations of human performance, yet it is often treated as something that happens only after the important parts of the day are finished. We work, study, exercise, socialize, use our phones, solve problems, and respond to responsibilities until the day is nearly over—and then expect the brain to switch instantly into sleep mode.It rarely works that way.Sleep is not simply a period of inactivity. It is an active biological state in which t...