I'm not a psychologist, but I think narcissism and self-importance simply stem from a small world view.

If your main hobby/recreational activity in life is smoking weed (certainly not judging anyone) then you'll likely only associate with people who enjoy the same things, if anyone at all.

This leads to a very narrow world-view where you're the center of that world. Going out and meeting people, doing different activities, taking on new jobs and roles, going to school and getting an education all really help to humble people and make people realize that most of us are all very similar in our pursuit of happiness.