I am not a great pool player. I am ranked as a strong BB in Michigan. I play league pool twice a week and find it very interesting when a player has a chance to beat me but at some point in the rack he realizes where he is and what is happening and I can see his arm start to shake and he hits a ball really bad and lets me in. I believe this is very common, most players cannot handle pressure because they play for nothing all the time. 2$ a game and eventually you should get tired of the 10$ to 20$ nights and start learning to play safe and steady your nerves. To handle pressure you need to be under pressure over and over and eventually your stroke will hold.
I kind of don't agree with your post if you are implying that gambling teaches you to deal with pressure.
Gambling, league and tournament play are completely different. Gambling to me has zero pressure. I just play and try to manage my money and be honest with my self about the game. But as far as pressure, none. I can afford to lose if I do. If I couldn't I would not play or at least not play for more then I could afford.
Pressure is self imposed, it is your personal view of the situation. Playing pool is not car racing or sky diving where I can get killed. Playing pool has no real dangers. It is just a game and fun to play. Now when it comes to playing in league or tournaments there is an element of added pressure. In league it is the sudden death nature of the play and the obligation you feel to the other players on your team. There is no room for error and you have to adopt a different mind set of play.
In gambling it is usually open ended and you can play as long as you want. A few bad rolls or lost games don't really matter and will not change the ultimate outcome. You know that as you are playing and I can tell when I am the better player. I have been wrong but not often. After a few hours of play I know if I will win or not. It may take a while sometimes. In fact I have play several days in a row before finally getting the guy.
Tournament play is a bit like league play except for the feeling of obligation to other players. It is your business and no one else's what you do. However it is sudden death and there is no room to just lose games and come back. You may lose to a much lesses player in tournament play. In that respect you may feel pressure to not make mistakes that you would not feel gambling.