I've already talked some about confidence and arrogance.
I go through an interesting confidence/arrogance cycle. I do the right "stuff" (personal and spiritual disciplines) and gain confidence. Then somewhere along the way, I think I have arrived and no longer need to do that "stuff." Now confidence has turned into arrogance and I am in trouble again.
Perhaps confidence is the main theme of Psalm 119. "Oh, that my ways were steadfast in obeying your decrees! Then I would not be put to shame when I consider all your commands." True confidence is unrelated to what we usually define as success. It is totally related to our obedience of God.
Oh, that I may find rock-solid confidence in the face of success or failure. The only footing for that confidence is God and his Word.