@netcan allow me to disagree. People make part of their choices partially basing them on rational reasoning (and, even for that part, mostly based on incomplete data and often faulty logic). But just check what works in marketing and you'll see how limited that rationality really is.
I mean "exists" in a pretty weak sense. If you present people with complex economic choices, they make rational choices and maximise their economic utility. IE if they are using second hand computers running hacked up linux to play movies on their TV and a good, cheap alternative presents at a lower price, most will eventually switch to that.
Describing them as such allows us to predict their behaviour.
