1. Scientists agreed it was impossible to run mile in under 4 minutes until Roger Bannister did it and then in decade following 336 people did. He did not let impossible stop him
2. Most famous athlete in the world David Beckham soccor reported that when he was 13 he was told "you'll never play for England, because you're to small and not strong enough."
He did not let others poor estimation of his ability deter him.