Some of my philosophy:
It's not foolish to miss-hit the ball - it's foolish to think it will never happen.
Don't get angry over a miss-hit, even the pros do it. They practice for hours and hours every day, and have been doing so for many, many years. Smile, accept it, and move on.
The only shot that matters is the one you are about to hit. Forget the last shot (although it's ok to bask in the glory of a good shot for a while). If you're not concentrating on the current shot, it definitely won't be good.
Remember the good shots, forget the bad shots. You're ALWAYS going to leave a few strokes on the course. Only remember these when it comes time to practice. Otherwise, remember the feel of that pure shot you hit onto the green, from the tee, out of the rough, whatever.
Golf can be very frustrating. You need to set realistic expectations or you'll drive yourself crazy. Don't expect to break 80 if you rarely break 90. No matter how good my round is going, I always remind myself I'm only a few bad swings away from 100. I don't do this to discourage myself, but to keep things in perspective. I rarely score higher than 100, but it can still happen. The more I think about things other than the next shot, the more likely I am to make a bad swing.
Don't forget, you're supposed to be having fun!!!