I believe that for instance Maurice Greene ,after all ,is rather humble. There is something in the way he talks sometimes ,and even his body-language that hints at him being humble.
John Smith says on one of the programs done for Eurosport that once your on top you cant afford not to be humble.
Well, then if we can name that many great athletes off the op of our head that are ‘nice’, then it seems to me that you answered the question…they are not diametrically opposed.
Confidence is important and that can manifest in many different ways. One thing that I see often is players who try to make up for lack of confidence or hide fear through anger or bravado. This is not going to contribute to success.