Everybody who fails to grow despite investing considerable effort fails to learn from his mistakes.
What is a mistake?
That is highly personal. If you solve problems at CT, for instance, then there are problems which you solve a tempo, problems that cost you an unreasonable amount of time, and problems that you fail to solve by coming up with the wrong move. If you compare yourself with somebody of the same rating, you will see that he has difficulty with quite different problems.
When you are clueless for a long time or even reach the wrong conclusion, we have a mistake at hand. Take for instance the following diagram:
I deviate a little from my own definition, since I found the solution just in time, yet I have the feeling I should see what is going on a tempo, and I do not. But that doesn't matter for the idea I try to explain. I just feel that these kind of positions take me way too much time. The reason for that is I have to calculate this position move by move, while I don't have an overall picture of what is going on.
The combinations in the position are pretty straightforward. If I want to learn from my mistakes, I have to find a way to defy step by step calculations, in favour for seeing what is going on in one go.
Verbal thinking can be of help here, but that is definitely not the solution. How can I simplify the position in my mind so that I'm no longer confused by my own thoughts about the position? How can I prevent that such such position takes me so much time everytime? How do I learn from my mistakes?