About my self confidence

I think I should be less confident of myself. High self confidence has ever been a problem for me, though I tried to limit it in recent times.
Yet deep in my mind there always is a part of me that thinks I have always true. And it ends up in calling my friend "a dreaming child" or so. As if I was a wise elderly person... I may also hint at my extensive knowledge of a lot of things (and it doesn't matter if it's real, or I just thought it up in my self confidence) and try to humiliate the other person...
What if I am wrong in my opinions? I was wrong many times in my life. How can I know everything I believe in know is true? And definitely I should confront the other's ideas in a less hostile way.