I think confidence is important to keep other players from getting a weak read from you and then just running you over with their aggressiveness. You don't want other players to push you around because you are too scared to make a call on a big bet. But I also think you need to be humble and take your time to make good judgements on your play and to think clearly about your reads on others. Without confidence, you will only win a tournament if you get really lucky. And you will also be terrible at late stage tournament play where people loosen up and are much more aggressive.