People can convince themselves that almost anything is true. This is because they're not entirely sure what the truth is. We're surrounded by enigmas and our existence is a series of unanswered questions. Since we don't know, we either ignore it or we cling to our favourite theory.
People say all sorts of things. They talk utter bullshit, regurgitating assumptions they've merely overheard and don't know how it ends. Still, they do it in tones which imply authority. Please, sit down and shut your mouth. If you're not sure what you're sure of, allow yourself to remain uncertain. You'll be better off than the other million people who overheard the other million.