As a younger man I played pool between 4 to 10 hours a day. An off day then was still pretty sporty against the locals. At age 60 I notice my endurance is weaker and my desire wants me to still have it. Concentration and focus seems to wander away from issue at hand (Getting it done on table). I have joined a group of much higher level players and I either get it together or look like I don’t need to be there. I have found out that it has forced me to spend more time at the table. I had to find time at least and hour a day at the table with what i call serious or good effort. After about 3 weeks and working on the problem shots that I kept missing I started actually competing. Then all of a sudden I felt that DESIRE start to happen. Do not get me wrong I make sure my EGO status is where it should and I am probably 4 to 5 on the leaderboard consistently in a group of maybe 25 - 30 competitors. In summary after attending ’ The Derby City Classic” for maybe the past 15 years straight I have noticed while watching the best in the world for 4 days that I will never be that good with what appears to be effortless running around the table and sinking balls. But, I did learn a little about how they stroked the ball and realize they put more time in than I do. In summary, My opinion as to get better making free throws, you must shoot more free throws.
A guess here but I think your mental game may need more polishing than your physical one. Your ego status may not be where it should be because you are trying to be what the social norm expects a person to be. Too much modesty, real or false, can be detrimental to your mental game. Your unconscious can't tell the difference between the two. Years ago I read a book about the mental side of poker. The author strongly believed that the ideal mindset to play poker would make you very unlikeable to others, even yourself. To win at most things, including pool, we don't have to be world class jerks but we have to be honest with ourselves and not lie to others, even the white lies we say for social comfort. I will occasionally make neutral comments but I will never say things like "I am here to donate" or "just filling out the field" if I am there to try to win. I very rarely say such things even if true, my unconscious is listening and if my conscious doesn't care neither does my unconscious and it is what drives my pool game.
While our physical game responds to practice, don't neglect the mental game. It can be the real stumbling block holding you back from that last little bit needed to win. I have found that not only does ego need to keep pace with physical capabilities, if it leads the way that can be a good thing sometimes for competition. I have known a double handful of people over the years with all of the equipment and all of the skills needed to win that never won. They didn't win the big events, they didn't win small events. They were always very close to the leaders but they never saw themselves as winners so they found ways to live down to their expectations.
Hu