Here the thing about thinking positive. If you spend time before the match feeling like you can win. And during the match you think that Tor partner is awesome. And believing that you are also playing well. Then you have spent 2+ hours in a great happy expectant mood.
And if you lose - well that's that. So what.
Pessimistic people spend much more time in the losing mindset - that's robs them of loads of pleasurable and excitable thoughts.