I've been like that with everything for most of my life. One trick I use is to allow myself to begin something without committing, or deciding that my next actions are going to be exploratory, making them non-concrete and easier to start.
Giving yourself license to change your mind gets rid of a lot of anxiety behind starting. I do have to balance that with the need to actually finish stuff, but I'm better off getting started regardless. Better to be in it and involved than sitting on the sidelines. Like some of the other comments have mentioned, making any decision is better than no decision, even if you later find it was the wrong decision.
Giving yourself license to change your mind gets rid of a lot of anxiety behind starting. I do have to balance that with the need to actually finish stuff, but I'm better off getting started regardless. Better to be in it and involved than sitting on the sidelines. Like some of the other comments have mentioned, making any decision is better than no decision, even if you later find it was the wrong decision.