Here's another piece of evidence from the field of tennis which shows what a big difference confidence and self-belief can make to one's performance.
From being number one in the world in 2008, tennis glamour girl Ana Ivanovic saw her ranking dropped to outside the top 60 early this year. But after claiming titles in Austria and Bali in the last three tournaments she played for the season, she climbed back to 17 and her career is finally back on track.
Ivanovic attributed her revival to a renewed belief in her own ability.
"It is a strange thing," she said. "Once you lose it (confidence) you feel like it is very hard to get it back... I tried to search for it in many different directions and many different places and with different people, but you realise that it is all the time within you, you just have to discover it."
This belief in one's own ability is similar to what Normal Vincent Peale said about "selling yourself on yourself" in his book Enthusiasm Makes the Difference.
But it takes more than just "discovering" the lost confidence. Ivanovic said she started working on her fitness with a close friend after Wimbledon. "Once I got fitter, I felt like it gave me confidence on the court," she said. "Once you start to feel better the confidence just grows and to have two titles at the end of the year meant a lot to me."
While we should start believing in ourselves in the first place, we must also choose the right course of action and work hard to produce results that will keep fuelling that confidence.
"I am very excited about this upcoming year," Ivanovic said. She has much to look forward to in 2011.
Haven't we too?