Improvement means the same challenge gets a different opponent.

The problem does not get easier as you improve. What changes is who it is up against, so the same difficulty that once beat you is now facing a more capable person and produces a different result. This is why it is worth returning to things that defeated you before rather than concluding permanently that they are beyond you.

Go back to something that beat you a few years ago and try it again with what you know now. Even if it still wins, you will learn something about how far you have come.