You might believe that positive thinking works for you, but it’s more likely that you’re being fooled by randomness. There’s a significant correlation between divorce rates in Maine and per capita consumption of margarine in the US, but that doesn’t make the two variables related.
Inevitably something happens that you perceive as bad, and your positive thinking comes crashing to a halt: “Ugh, I must not have been thinking positively enough!” It might be better to stop thinking altogether, observing your outcome with nonjudgmental awareness: “Oh, how interesting!”
Put positive and negative thinking to the side, know your desired outcome, and let your body do its job.
[Major h/t to W. Timothy Gallwey; his classic The Inner Game of Tennis is a boon to any performer across sport or life.]