Surprisingly, fatigue may boost creative powers. For most adults, problems that require open-ended thinking are often best tackled in the evening when they are tired, according to a 2011 study in the journal Thinking & Reasoning. When 428 students were asked to solve a series of two types of problems, requiring either analytical or novel thinking, their performance on the second type was best at non-peak times of day when they were tired, according to the study led by Mareike Wieth, an assistant professor of psychological sciences at Albion College in Michigan. (Their performance on analytical problems didn't change over the course of the day.) Fatigue, Dr. Wieth says, may allow the mind to wander more freely to explore alternative solutions.