Maybe I should rephrase my original question.
If there are 3 players of equal skill levels, and there is a prize of $100,000 for the player who can improve the most in 1 year what should that player work on, and what should he not waste his time on? Forget the fundamentals, let's say they're pretty solid players to begin with, but are stuck at their current level.
That's a whole different question. There's 2 different parts of the game, 1 being the ability to control everything from the cue ball back, and 2 your knowledge of what to do, when to do it, and when not to do it, being the game you're playing. Without the skills to control the cue ball, it don't matter how well you can play the game in your head, if you can't make the shots, and 2, it don't matter how well you can make the balls if you don't know when, and how to defend your game, and when to go for the win, and exactly how to accomplish that goal.
But, the first place you start is from the cue ball backwards, being you, the machine operating your cue stick, the control of the cue ball to make it go where you want it, need it, to go in order to keep making the balls, by not missing a shot when you NEEDED to made it.
Then comes to ability from the cue ball forward, the knowledge it takes to know when to pocket a ball, when NOT to, how to tie up balls when needed....the list goes on and on. Then you need to be able to, on top of everything else I mentioned, have the insight to be able to read your opponent, know his weaknesses and his strengths, and when to stay away from one, or attack the other.....the game of pool is mastered by LIVING it, not just playing it.
Playing in the ZONE is living the game, in tune with it, feeling the balls and table as you're playing, your cue stick is an extension of your fingers and hands, you're just holding on, there's nothing you can't do....until that one little thing distracted you....and you miss, question is, did that miss cause you to lose, because what do you think your opponent is doing at that exact moment you missed, what do YOU think he's thinking? Do you really think you have any different goals than HE does?