I usually have to take a break from practicing for a few minutes. I eventually come back to it but mastering something that demands a lot from you also requires a significant amount of failures. Creativity block for musicians isn’t the same as artist or writers. It is not that we fail to conjure up content, it’s that we fail to be productive because of the lack of motivation or from the amount of frustration. Not being able to complete the difficult runs or rhythmic patterns is genuinely disheartening, but that same feeling can be motivation that pushes you to do better (for some). That feeling I was describing before is what I usually experience. I do not consider myself the best musician, so whenever I have a difficult piece I’m sure to turn my difficulties into inspiration and motivation. Some tricks that I do is to listen to a professional recording of the piece I’m trying to perform or write down notes to help me. Any little mistake ruins the whole song so I try to not let any common mistakes through and prevent any random new ones.