In poker you need to be confident or you risk being eaten alive at the tables. You need to have confidence in your ability to read players, confidence in your ability to make bluffs and confidence that you can beat the game you are playing.

Whilst confidence is vital, over confidence is more dangerous than having no belief in yourself at all. Being over-confident and cocky will make you over estimate your abilities and risk taking bad beats personally and therefore going on tilt is a likely possibility.