Perhaps one of the greatest examples of this was the belief that running a mile under four minutes was humanly impossible, a view reflected by the hundreds who tried and failed. However, Roger Banister decided that this daunting physical barrier could be overcome. After he smashed the record in his exhausting, historic performance, people immediately believed that it was now possible and in the 18 months after his historical achievement the sub 4 min mile was achieved by more than 45 runners.
Research has also shown that many of the people at the top of their professions strongly believe that they are better than they really are. But this belief allows them to BE better than they really are. And the more successful they are the more evidence there appears to be to support their belief in their greatness.
It is also worth pointing out, that one of the functions performed for us by our mind is the validation of our ways of thinking about the world. We will tend to seek confirmation for what we believe, even if those beliefs are harmful to our wellbeing and better good. If you believe that you are capable and confident, you pay attention to those signals from the outside world which reinforces those beliefs. If you believe that you are not as good as others or that you are being judged badly, you seek the confirming evidence just as readily. When this happens, often at the first sign of difficulty in achieving an objective, we are more likely to abandon our plans and shrink back into our comfort zone.