But if you just keep trying, you'll get better. You have to crawl before you can walk or run. You could be having a bad day, as everyone does. Maybe you have other stuff on your mind, such as school or friends. Or perhaps you've entered a new, harder level and haven't quite mastered it yet.
Experts say it's like being a mountain climber who gets stuck on a plateau, a wide flat place.
It takes time to scout out a way off that plateau. Shake things up. Try to find something new and fascinating about it. If you don't like it or it's too hard, talk with your teacher about playing something else. Or shake up your practice routine.