I make things way too hard for myself and try to make virtually everything from scratch, which I guess is good in the long run, but it makes "the long run" about 50 times longer. I take like 3 or 4 months to finish a track because of this and because I tweak little pieces of tracks in ways barely anyone would notice for weeks at a time.
Also I have fairly consistent struggles with self-confidence when producing; I compare my songs to my favorite artists and think, "How the hell did they do that, I'll never figure that stuff out." I've gotten better about this recently, but I still fall into that mindset sometimes. It's pretty toxic when you're trying to be creative.