I suspect that nearly everyone "justifies" what they believe via their own experiences. We grow up being told that this and that are "true", but I think most of it remains just theory to us until we experience something in life that causes us to conclude that some learned theoretical truth really is true. We don't all get taught the same theoretical truths, though, and we don't all have the same life experiences, of course, so naturally we won't all come to the same conclusions about what is and isn't true in life. But, we can share our ideals and experiences with each other to maybe learn something from each other.