It's all about training.
You will NOT "rise to the occasion". You will REVERT to the level of your training. If your training is minimal, so will your performance be.
This also means your training needs to be realistic and needs to use the gear you'll be carrying, abd in the same way you would in a real-world situation. If not, the results can be disasterous.
A couple of good examples from Massod Ayoob (regardless of what you think of him):
Back when most cops carried .38/.357 revolvers, many police ranges did their best to retain used brass to be reloaded for training. At one range, they had a bucket at each stall, and officers would fire a cylinder of ammo, then toss the brass in the bucket and reload. One day, one of their officers was involved in a firefight. He fired his gun dry, and went to reload.
Because his "training" had taught him, through many trips to the range, to toss his empties in a bucket at his left foot, the officer, in the middle of this firefight, had stopped and was looking around his feet for a bucket! It sounds crazy, but this was a part of his shooting routine, and became automatic. Luckily, the officer was able to "break-out" of his training and finally reload, but his poor training habits could have gotten him killed.
In a similar story, another department issued pouches, worn on the left hip, for officers to carry loose ammo for their revolvers when on duty. But at the range, they were instructed to put the ammo in their front-right pants pocket. So, during a firefight, an officer tries to reload, and instead of going to the ammo pouch, his hand immediately goes into the front-right pants pocket, where the officer begins to produce keys, change, and everything but ammo. He was nearly killed before he overcame his training.
-Troy