The worst thing is when you're paralyzed because of disappointment. Not that you're afraid of acting because you yourself might be disappointed by the result, but rather because you fear disappointing others. This is a particularly difficult cycle to get out of, especially if you don't snap out of it quickly.
It goes a little something like this:
1. You're worried about attempting something that you're not particularly confident in. Perhaps you try it a few times and it doesn't turn out so well, which shakes you even further.
2. Someone, usually with good intentions, notices that you're not doing as well as you should be, or that you seem upset, or any number of things. They figure out, or you tell them, what you're having a hard time with.
3. They ask to see you give it a try or work with them so that they can help you improve.
This is the most difficult part, and I've noticed that it's generally the turning point. If you agree you can work together to identify the problem and improve; maybe they can just be there for you when things are hard, and help you through it.
If you don't/ can't try...
4. You can't bring yourself to work on it or try, because you feel like they will see how bad you are at this thing. You will reveal that you're somehow some sort of fraud, and that you don't belong here. That you've cheated your way to whatever it is you're doing. They will look at you and be disappointed.
5. This is especially difficult if it's a person you feel particularly beholden to, or if it is a person who's put a significant amount of time into helping you get better. In fact, the more they tell you that they believe in you and you can do it, the more guilt you will begin to feel for not being able to live up to their expectations. For being a failure. If there was a chance that you could work with them to improve before, it's much slimmer now. The very idea of showing your failings fills you with anxiety and fear. You can only avoid or apologize.
6. The feeling carries over to other days, and adds up over time. Each time the person, or people, come and try to help you remember the previous days; you remember how long it's taken you to be able to do this thing, and anxiety washes over you. You can apologize and avoid. If you avoid, maybe you can get better at it while they aren't there. Maybe you can improve without them seeing you fail; without them seeing how long it's taken for you to just keep failing. You cannot accept help, because then they'd know how awful you were, and they would be disappointed. The longer you go, the further behind you are, the more you have to hide and run. Apologize and avoid.
Fear of failure is tough enough when you are your own worst critic. It's significantly worse when you believe that you're letting someone down.
Just remember, it's still you. These people don't know that you think you're letting them down. Most of the time they don't feel that way at all.
Self-doubt and fear can ruin pretty much anything if you don't notice yourself spiraling until it's too late. Catch it early.