... and how long you can maintain good concentration when practicing. Because if you find yourself slipping into sloppy practice, in my opinion, bad practice is worse than no practice at all.
I would assume if you find yourself having a "sloppy" (bad practice) session then your
mindfulness to the repetition and improvement (performance skills) of specific pool shots is at issue. How many times has the question been raised, "What is the secret to playing great pool?" I maintain that the answer is "practice, practice, and practice." And through practice, we gain confidence and ultimately success.
What do you do when your playing an opponent for some green and you lose repeatedly? Ordinarily, the losing player becomes noticeably "sloppy" in his thinking and execution of shots. The losing player has lost his "mindfulness."
If the losing player cannot refocus with concentrated attention on every shot, then he should quit the game. The same with practice. Although pool tables are on four legs, they never walk away. Today's bad will be tomorrow's good.