Some people at the poolhall will only play people of their level and below. They completely avoid stronger players, even with appropriate weight. I've seen these people play for the last few years and none of them have improved by any marginal difference. My game didn't start improving until I played against good players, and when they all stopped coming to the old poolhall I went into a very long slump. What I learned is that when you play someone who is really good, most of the time the mistakes you make are magnified. This doesn't even come down to just missing balls or missing a safe. It comes down to not playing a GOOD ENOUGH safe. If a strong player is not running racks but he is beating you, it's because he is controlling the table. When you play weak players you get used to getting a chance to control the table often. Against strong players you will quickly learn that even them getting a lucky safe after missing a ball or hitting a kick is HUGE. This simple factor can reflect the outcome of a few games, or even the entire match. This is also where the break becomes so important in 9-ball. People hear that pro players break and run out 15 or 20% of the time, so they think "What's the big deal about the break then?" If someone is consistently making a ball on the break, even if they don't get a shot, if they can see the low ball they can control the table, and you may not get an open shot. You've got to make the best out of your trips to the table with kicks or across the table frozen to the rail. Against weak players nobody cares about kicking at the 1-ball, you are almost guaranteed another chance to return to the table. If you play against weak players long enough and you get used to this, your game will never improve, because you will never have the initiative to really bear down on EVERY SINGLE SHOT. People don't want to play strong players because they don't like getting beaten into a pulp, which is understandable, but they don't realize how important those beatings are in the long run. If you get drilled enough you are going to start wondering what was the shot that could have turned it around for you.