Human brain is subjected to social influence a lot. So as people start mixing with others or in other words comes out of its well it changes its opinion. Understanding of the outer world better also leads to change in beliefs. When you'll flip through the pages of history you can get ample proof of the fact that beliefs change. Take for example Elizabeth Warren who started as a conservative but later changed to a democrat(liberal icon). Though there are people who don't change their beliefs but maximum does.