A most brilliant excerpt from Tversky and Shafir, Psychological Science 1992

It is difficult to overestimate the significance of the tendency to delay decision. Many things never get done not because someone has chosen not to do them, but because the person has chosen not to do them NOW. 

To illustrate this point, we offered students $5 for answering and returning a long questionnaire by a given date. One group (N = 56) was given 5 days to complete the questionnaire, a second group (N = 58) was given 3 weeks, and a third group (N = 57) was given no definite deadline. 

The corresponding rates of return were 60%, 42%, and 25%. 

Thus, the more time people had to complete the task, the less likely they were to do it. [… The] addition of time enhances the tendency to delay action.