Read this about Roger Bannister:
“In 1954, Roger Bannister broke the world record and ran the mile in
under 4 minutes. In the whole of the history of the human species,
no-one had been able to do that. It had been considered impossible -
beyond the physical limits of the human body. Year after year, runners
had come closer and closer but no-one was able to break the 4-minute
Not only did Bannister practice and train, he constantly rehearsed
the event in his mind until he truly believed that he could do it.
Even though nobody before had been able.
Yet, within six weeks of Bannister breaking this psychological
barrier, it was broken again, and within a few years the mile had been
run in under 4 mnutes hundreds of times!
Belief holds us back more than anything else – far more than fear;
more, even, than physical constraints.”