Often times the solution to a difficult piece of repertoire or passage seems to be hammering on it again and again. Or trying to get as many perfect repetitions in as possible.
But our fingers get tired; we make mistakes. Our mind gets fatigued, we loose focus, and we make different mistakes.
Sometimes what’s really needed to improve a passage or piece is some space. That may mean putting a piece aside until the next day right when it feels like a breakthrough is around the corner. It could mean coming back to a difficult passage a few days later with fresher ears and fingers.
One need not hit a wall to see how a bit of time off can help.
As an experiment, instead of hammering a difficult passage over and over again shoot for a set number of repetitions. The number of repetitions should be enough to work things out but not enough to be mentally or physically fatiguing: remember the goal here is to get the passage perfect a set number of times. This might mean simply playing a passage at tempo if that can be done without mistakes or applying a practice technique to it.
Once the last repetition is complete, put the passage away and don’t touch it again until the next practice session or the next day. Then do it all over again for a few days and see how that passage shapes up over time.
It’s easy to forget that musicians are working on a large time scale when we learn music. A piece doesn’t come together in a day — even the most virtuosic player who can read a piece perfectly on the first go will find things which they can really dig into and improve. Take advantage of the time. Use the breaks from a piece or passage to work on different things without getting stuck in a loop of frustration and stagnation.