You are out of your mind if you think people can reliably tell what they want. Sometimes they can, sometimes they can't. Telling the difference is hard, but it's pretty clear that they can't when they suffer from the serious mental condition called depression.

During a lifetime, your perspective and world view will change completely - multiple times. Young people have no idea, because they haven't had the chance to experience it yet.

I never claimed that people could. People make choices that negatively or positively affect their entire life and that is a part of life.