I tell a player when I start working with them that there is a strong likelihood that they won't break a sweat in one of my workouts for a couple weeks, maybe even a month. This usually draws concerned or confused looks from players that pride themselves on pushing their bodies to the limits. I make clear to them that we will be working hard, just a different kind of hard work than they are accustomed to. Relearning or changing shooting mechanics is a trial of patience in the beginning and this is where is see a lot of coaches falling short.
I saw a coach do a great visual exercise that I now use all the time. On a cardboard box he marked a point with a pen, then another point about a foot below. He explained that the first point is how we start any movement (like shooting) and the second point is how we finish that same movement. He then jammed the pen into the cardboard at the first point and dug a jagged, indirect path to the second point.
"Let's imagine this is how your muscles fire to create that movement, but that this is where you make your mistake," pointing to a change in the direction of the groove.
"If we keep making the same move at the same speed, or try to make a different move quickly then the pen just stays in the groove and strengthens it. What we need to do is slow down, find the area of that mistake and live in that area, learning to redirect the pathway."
As he explained he slowly started to gauge a new path from at that change of direction. Slowly the new path got deeper and longer, and he was able to move the pen further up the path to get a "run" at the next path, making it deeper still. With time he was able to change the path that the pen followed and get into out of the original, flawed path.
I've seen a fair number of coaches that are great at identifying the problem area in a players mechanics, but far too many simply tell the player the problem and expect them to fix it at game speed. When players are unable to correct the problem, both sides get frustrated and they give up assuming that you can't teach old dogs new tricks.
One of my favorite stories is of a college player that I worked with. The player was about a 45% free throw shooter, and in the beginning of the off season we started to rebuild his shot. During the first workout he air balled half of his shots from well inside the free throw line. That continued for a couple weeks, which is a longer than I expected. Two more weeks and still the air balls continued. Being totally honest I was starting to doubt if he would ever get it, but I knew what the error was and so we remained patient.
In late June, two months after our start, he started to get it. The success started to snowball. The habits started to get strong and stronger, and the results came along with them. In late August I was caught with two players in one workout and towards the end I broke them into two hoops to shoot free throws. My guy seemed to be making a fair number of shots, and was shooting them well, so I moved to the other hoop. I kept looking over to see how he was doing and he seemed to be shooting them well and making a pretty good number. I called across the gym "stop when you shoot 100", and he nodded. About 8 minutes later I was back at his hoop as he said "last one" then swished the ball through the net. "How many did you make?" I asked. "94."
You never know how long it might take to get it. It varies for every person and every habit, but you can't skip steps. Identify the problem then work as slowly and as diligently as possible to do it correctly. As you are able to do it correctly, then slowly start to add speed and range. If the player struggles at a certain level, you slow down slightly and strengthen the habits.
As coaches we need to have and understanding of the problem and a plan to improve it. If a player is struggling to transfer skills from one level of performance to the next, then as coaches we need to find a drill to bridge that gap. That is the whole point of drills - to put players in a position where they can learn a slightly more difficult skill. If there is too big of a gap, that acquisition of the new skill will never occur. Invent drills and get creative. A player can execute the habit at 6/10 of difficulty, but not a 7/10 -- then you invent a drill that gets them reps at 6.5. Add layers to drills, build slowly, but DO NOT SKIP STEPS.