It’s about having a strange combination of high expectations for yourself, but for the things you’re capable of doing. It’s kind of unreasonable for you have high expectations about things that you have no business even trying, for example: “I’m mad at myself because I tried to run a marathon today and it didn’t work out.” There’s no reason to think that you would be able to do something that other people have spent years preparing for. It’s not realistic, yet you beat yourself up about it, so then you feel incapable of doing other things.
Go a little easier on yourself, and in so doing, be prepared to make and do things that might seem silly at first. Just keep moving: don’t ruminate and stare at the wall. Don’t just play with your phone: go out and produce something.