I try to keep the question "What do you know, and how do you think you know it?" in my head as much as possible (I think I picked it up from Harry Potter and th

I try to keep the question "What do you know, and how do you think you know it?" in my head as much as possible (I think I picked it up from Harry Potter and the Methods of Rationality). I mentally recite it a lot, often without really thinking about it. Every once in a while, though, the thought catches me as I'm recalling some long-known fact, and I'll realize that I don't have a good reason to believe it. Many of these are things I was told long ago by friends/parents/family/teachers and stored away, their sources forgotten. The maxim has proved useful in unlearning things I was too young to disbelieve when I learned them.