If you surround yourself with like minded people, you are more likely to accept the group view. Parents typically hold a lot of sway over their children. Religious schools, religious colleges, NRA, political party membership, also fall into this category.
Ronald Regan before he married his second wife was a Democrat. His second wife and more importantly a rich father in law influenced Regan to switch to become Republican.
Being a part of a like minded group can to some extent cement a person in place from reviewing the basis for their beliefs and looking at the facts from a fresh perspective.