Practice benefits from this delusion.
You don’t show any tangible improvement via practice from one day to the next. It’s only over time that the practice starts to become evident.
So it’s perfectly lucid to think along these lines: “This practice doesn’t help. I’m not good at this now, and I’ll never be good at this.” (Side note, our current education model reinforces this idea by rewarding students who have innate abilities and not supporting those who take more time and practice to master a skill.)
It’s delusional to think, “I practiced, and I got no better. But I’m going to get better if I keep practicing.” In this way, practice is the textbook definition of insanity: “Insanity is doing the same thing over and over again and expecting a different result.”
But without that delusion, you’d never keep practicing. And without practice, you really won’t get better.
It’s the helpful delusion.