You know you can play good golf, but when you play in tournaments, how do you play? If you don't play as well as you think you could, it may have to do with your mindset going into the tournament. It is easy to put extra pressure on yourself because you want to prove something to yourself and others that you can compete and win. You are essentially amping yourself up and making the tournament into something very big in your mind because of that. If this sounds familiar, you may want to work on rejecting those type of thoughts.
Dr. Bob Rotella talked about this in the clip below:
"Find peace on the course.
When you practice hard and admit to yourself that you really want to win, it's easy to build up a tournament into something so huge that you can't play. I've seen amateurs not used to competing arrive two hours before their tee time and try to rebuild their golf swings. They become panicked practicers and try to perfect every area of their game. They get themselves so tied up in knots it's ridiculous. Tour players do this, too. I've seen guys come to Augusta, rent a big house and invite their family and friends. When Thursday comes around, they start worrying: What if I miss the cut and disappoint everyone? The golf course has to be your sanctuary, the thing you love, and you can't be afraid of messing up."
This is so spot on. The best way to do this is to go out and have fun. Be grateful you are on a great golf course, on a nice day, playing the greatest game, and the unnecessary pressure you are putting on yourself will dissolve. Those bad thoughts will vacate your mind. Work on it and see if your tournament play improves.