You should also know when to walk away, and when to run; but that’s not the point of this post. Rather, it’s about when to stop training. Training skills requires a considerable amount of mental focus, just like any other athletic endeavor. Focus is especially important in the shooting sports, because you’re dealing with a lot of complex body mechanics.
All of the stuff we do that are “shooting tasks”: aligning the sights, pressing the trigger, reloading, etc are fine motor movements. The closest we get in the shooting sports to a gross motor movement (aside from running between shooting positions) is drawing the gun, and even then the act of grasping the gun correctly at speed is a fine motor skill. It’s a myth that you can’t execute fine motor skills under stress, but training those fine motor skills to operate well under stress takes focus.
Which is why I’m a big believer that you should stop training when you can’t focus on the training task any more. Let’s say you’re dry firing, and you’re working on drawing the gun and establishing an acceptable sight picture in less than 1 second. You’ve done a few really solid reps, everything feels good, and then you get a text from your girlfriend/wife (or husband/boyfriend for our lady shooters). You deal with whatever the distraction was, and then go back to practicing…and all of a sudden your reps are crap. You’re missing par times, flubbing motions, or whatever it is – and all that happened was a simple text.
It’s probably time to stop whatever it is you’re doing and take a break. You don’t necessarily need to end your training session right then and there, but it’s advisable to take a second to get your head back in the game. If you’re not focused on the training task 100%, you’re doing yourself a disservice and you’re not getting the most out of your training.
When I’m training, I like to train in a “clean” room – no TV, no cell phone, no iPad. Maybe a little classical music in the background, but that’s really it. I want my mind clear of distractions so I can give 100% of my attention to increasing my personal levels of awesome.