Oooh this is a great topic!! Most people only focus their brightest moments, when really its how we handle our failures that takes us the furthest. (Sorry for being cheesy lol...)
There aren't many projects that I've hated, or at least not that I've hated and still finished. A lot of projects I've been really frustrated with, but liked them after they were over, or once I got past a certain point. Often if I really really hate something I'm working on I will scrap it. Your time and your mental health aren't always worth the results, especially if your heart's no longer in it. Now that I'm older I try not to delete everything though. Sometimes you can come back to an old sketch that was garbage months or years ago and make something out of it with that new perspective.
Sometimes you have an obilgation to finish the project, however. For me this happened with a tarot card I made for the Homestuck Act 6 Tarot. I did two cards: one of them, 2 of cups, was one of my top choices and I was thrilled to make it. The second one, 10 of swords, was one I volunteered to do because the previous artist left the project. It was an okay prompt for the card, but I was having a difficult time with the pose... I ended up getting burnt out with it and it had a lot of technical issues. Stylistically it also didn't feel as "me" as my 2 of cups card. (In hindsight I wish I'd kept the original design for it, rather than the one that ended up being official and printed, but live and learn.)
(from left to right: cups version 1, cups ver. 2, swords ver. 1, swords ver.2)
A different example is a project that never got started: Someone here on the forums was looking for a collab, I tried and it just went no where at all... So instead I got in touch with my good friend (who I've collaborated with before) and we made this ridiculous poem.