It's a common phenomenon - you look at a puzzle, fail to solve it, then look at the solution and move on. Then come back to that same puzzle some days later and still can't solve it/remember the solution.

So it's questionable whether you really learned anything the first time. If the exact same position showed up in your game, you'd probably have missed the correct move.

That's ultimately the purpose of repetitive training systems like spaced repetition and the woodpecker method (which is somewhat different from spaced repetition, actually).