it's because people have the irrational belief that their thinking and reasoning more about a problem/decision makes their outcome better.
I think the common symptom found in software is design analysis paralysis. A software team end up using tonnes of time fretting about design choices (often as a committee), rather than just use that time to implement one of the designs. The (ir)rational idea that by reasoning about the design up-front, one saves the (potential) time lost in reimplementing a different design in the future!!