Success breeds success. Once an athlete has significant success, their confidence tends to grow and they tend to perform better. This is quite apparent where Eli Manning is concerned.
Interestingly, in addition to being more confident on the field, he appears to be much more comfortable and more confident with the media.
Building confidence is central to my work with atheltes and the kinds of things we do at www.stayinthezone.com
Our stay in the zone program focuses on confidence.
https://stayinthezone.com/get_stay.htm
My new book Get Into The Zone In Just One Minute also deals with confidence and self-confidence in addition to many other performance related topics.