Many coaches and players try to fix problems by fixing the symptoms. In many ways, this is what separates a good, experienced coach from, say, a top player who knows proper technique but isn't that experienced in coaching it.
Here's an example. Suppose a player tends to fall back as they loop forehands. The "simple" solution, of course, is to tell them to focus on rotating around and forward into the ball, i.e. "don't fall back." And many coaches try this many times, and it doesn't work – because they are treating a symptom of a problem rather than the root of the problem. The real question is why is the player falling backwards – and the answer almost every time is that he's too far from the ball, with his left leg too far from the table. And so he's forced to reach a bit forward. The falling back is to keep his balance. Solution: Have the player stand closer to the ball, with the left leg closer to the table. Then he'll have a natural rotation into and through the ball, with no falling backwards and off balance afterwards.
Here's another. Some players struggle to rotate their body backwards (to the right for righties) on the forehand. The more they try, the more awkward they look. I've seen coaches struggle with this, not being able to figure out why the player has so much trouble with something that's so easy for others. And so they'll keep telling the player to rotate more on the forehand. But the player simply can't do the rotation comfortably – the symptom of a problem – because they haven't fixed the root of the problem – which usually is their knees are facing forward. If you watch top players, the knees point somewhat outward in their ready stance, which allows easy rotation in either direction. Here's an example – see how the knees point somewhat sideways, not forward?
And here's another. Often players struggle to get great spin on their serves. Rather than converting most of their energy into spin, and getting slow but super-spinny serves, their serves go long, with only moderate spin. Often they are told to graze the ball more, but when they try, they are unable to do so – because the inability to graze the ball is a symptom of a problem, not the root of the problem. The root of the problem usually is they are contacting the back of the ball, often toward the top. If they want to graze the ball more, they need to contact more under the ball and more on the side. If the player doesn't change his contact point, he'll continue to struggle to graze the ball as his racket will be approaching the ball too directly to graze the ball, resulting in a flatter contact. You can still get moderate spin this way, and many players (and coaches) settle for that, never realizing how they are limiting themselves.