I have noticed that when I go into a round or tournament with high expectations, I play terribly. When I go in with no expectations at all, I play great.
I also noticed that if I have a five-foot putt or less, I have expectations of making it, but I struggle with that range and I get very upset when I do not make that putt. When I have a six to 15-foot putt, I have minimal expectations, and I am indifferent if I make or miss the putt, and for that reason that is my best putting range.
I believe there is a direct correlation between great golf and having no expectations. Golf is a crazy game because of that. In life, it is good to have high expectations, aim high, think big, etc. But in golf, it is best for me to expect nothing, think minimal, and stay in the moment.
I can say all of my best rounds involved minimal expectations. For example, I have had back issues and played rounds with back spasms. I went into those rounds with the thought, "this will be some interesting golf, I hope I can break 100!" but I played some of my best golf shooting close to even par with that thinking. For me, it is calming and brings out the best in my game.
If you feel like you go into each round expecting greatness, yet struggle, try going into your next round not expecting anything at all and just have fun. It might open the door to better golf.
"Act without expectation" - Lao Tzu