Horn players know this story all too well. To get those high notes there is a natural tendency to push the mouthpiece hard against the chops. Often times too hard to the point where you regret it later. Players know that more mouthpiece pressure can help to support weak or tired chops in order to continue playing. The downside is that too much pressure against the lips prevents proper blood flow and you wear out even faster and finally it's game over until you've had plenty of time to rest.