Oh god, I know this feeling like the back of my hand. It still happens to me on a daily basis. Yet, instead of being a skilled artist/designer, for me it's writing. I'll go back, editing my grammar, realize how stupid something sounds, edit it, then realize it doesn't fit with the other conversation, edit that, then scrap the entire thing because the edits won't add up and it would be better if I started over.
Writing comes easy most of the time for me. Art... *imitates a gun blasting my brains out* As much as I love it, I could draw a picture twenty times and not be satisfied with it. Still not satisfied today.