Ask HN: Why do you spend time comparing stuff/optimizing choices?

Whenever I set out to buy anything (physical good, web app, iPhone app, etc), I can't resist from spending hours comparing every single option, working out which is best. Why do I do this? I can't stand knowing that there could be something better, whether it is mine or someone elses money being spent. Who else does this? And why do you think you/we do it?