Bowling can be a game of emotions. If you let your emotions affect your attitude toward what you are doing, more than likely, it will impact the outcome of your game (this is actually true in most aspects of life as well).
If you have a negative attitude it will cause you to bowl worse. The worse your attitude gets, the worse your bowling gets. If you throw a bad ball, or get a bad break on the lanes (i.e. a 7-10 or 8-10 split), you have to shake it off and not let it impact your bowling. That is much harder than it seems.
If you keep your attitude positive, it will help you to bowl better. By keeping a positive attitude, you can improve your average or at least maintain it. If you are having a “bad” night (i.e. not bowling your average), keeping your attitude positive will allow you to bowl the best score that you can on the condition that you face, thus keeping your average higher in the long run.
If you have a bad night, you want it to be as good as you can possibly make it so that it doesn’t affect your average too much. After all, if you keep your pin count up, your average won’t suffer as much.