People generally feel more comfortable when they belong to a group. To belong to a group you usually have to follow certain norms. People do not want to be viewed as the outcast or the weird one. Sometimes people dismiss their own views or ideas because they don't think it will be accepted by others. When your ideas or beliefs are different from others you begin to question them yourself.
You usually think that things are right when other people, or the majority of people, are also doing them.