When I first started I made the mistake of making a T-Shirt quilt for my husband.... it grew into a massive, bigger then a California king, sized quilt. He had been a roadie for years and I used shirts from his favorite artists that he had worked with.
Never Again. I did finish it. But it could use some additional quilting.... it could be so much better. But I just couldn't deal with it any more. So done is done. And now I know that I will never make another T-Shirt quilt again and why they are so expensive to have made. And it's not even a comfy quilt! All the decals on the shirts make it not good for curling up with.
I also sometimes start a quilt and then realize that I just don't like it or it's to fiddly for me. I then use the blocks that I have finished to make backings for scrappy quilts. Most of my quilt backs have an assortment of random blocks.
For your next project start something smaller. Make a crib quilt or throw. Don't pick a really complicated pattern. Also... don't be so hard on yourself. We've all been there and it's fine.