Margaret Thatcher, who was known for sleeping only four hours a night, is often credited with saying “Sleep is for wimps!” But sleep is actually work. Putting down the phone, setting aside personal or political worries—these require…

Margaret Thatcher, who was known for sleeping only four hours a night, is often credited with saying “Sleep is for wimps!” But sleep is actually work. Putting down the phone, setting aside personal or political worries—these require…