It's ok not to be great at everything. If you try, you will succeed at nothing. I believe it is a huge myth that we all can do anything we set our sites on. However, no one is built to do everything. I do believe, however, that we all have the potential to be great at something. Prioritize your greatness. Pick a few things that you truly want to be great at, and go after them.
If you don't prioritize your greatness, you will drown yourself and nothing will turn out right.