"One day's happiness often predicts the next day's creativity." (Teresa Amabile)
Esoterica: Those of us who think we create best when under pressure or when meeting deadlines should think again. Amabile found that "time pressure stifles creativity because people can't deeply engage with the problem. Creativity requires an incubation period, people need time to soak in a problem and let the ideas bubble up." You can read management guru Bill Breen's famous interview with Teresa Amabile here. A note of caution--none of the subjects of Amabile's now classic research were crows.