Proper training is an unnatural act and requires intellectual understanding and control. We need to understand that proper exercise is not painful, it is simply effort. We need to realize our goal is to stimulate results, not to demonstrate suffering or impress others.
Refraining from screaming, grunting and grimacing is also important for sound physiological reasons. Such behavior is one of the major thieves of exercise effectiveness.
Finally, by understanding some neuroanatomy, we can realize there is a valid reason to avoid grimacing, vocalization and excessive gripping.
Stoicism will improve your training.