Thus, they are associating with people who share their attitudes and who influence their attitudes and behaviors. We pick our environments based on our beliefs. We are only to explain why behavior is consistent or different across situations. People seek rewards and avoid pain, so there must have been some rewards with being a hippie and a yuppie. Indeed, there is.
Some people love to eat red hot chili peppers.
They actually burn in your mouth and release endorphins to kill the pain. People are motivated by survival for themselves and their offspring. The goal is to have children with a healthy mate. OR eating red hot chili peppers can kill or weaken the immune system. These people will not likely find a mate and will die off over the generations.