The more time you spend on a skill the more critical you become about it. Not only on yourself but on others too. The moment you start seeing flaws on everything it becomes a passive job to fix it even though it's not neccesary. You overthink, you spend more time thinking about the results than the process itself. You start beating yourself up comparing your productivity now to the one in the past because before it wasn't tied to quality but to the process of creating. I discovered this everytime I picked up a new form of art and I wasn't critical about it. Because I had nothing to compare it to. I think there is no easy solution for this, just turn off your brain while you are drawing and try to enjoy the process of giving form to something that was inside your head. It doesn't have to be perfect, it just has to exist.