I realy support you in your observation. Indeed, pessimistic people can't achieve something they want and it's not only about sport...
Even my real-life situations showed me that it is very important to set yourself on success, otherwise everything will be failed you can regret about it..
This world will be better when most of us will believe in ours success and will try to do everything to develop yourself. In this way, people must be optimistic and be happy of doing everything and your work will go up quickly!