Whenever I hear about people saying they have "art block" they don't seem to elaborate on it much and this kind of seems to suggest that there is only one kind of "art block" but I don't think this is really the case, I think that an art block is probably just anything that sort of inhibits us psychologically from making more-- It develops from some sort of internal cognitive dissonance that pulls but also pushes at the same time, resulting in frustration and eventually giving up.
My biggest and most frequent "art blocker" is the idea that whatever I make just isn't going to be good enough: That it won't get enough favs, that my client won't like it, etc etc. I think this is an easy one to fall for, but it's also the most frustrating because if you don't continue to make something it becomes self-fulfilling if you don't try to work through a piece. I think this one happens because I must have convinced myself at one point or another that unless I was some prodigy at whatever I am trying to do, there is no point in doing it at all, but this isn't restricted just to art making and seems to spill into all kinds of crap I do.
I also get a much less frequent one which is kind of hard to explain. Basically it involves realizing that I've put a lot of hours of effort into arting, and a lot of people have gotten some enjoyment out of what I made, but I haven't been directly compensated for their enjoyment. And when I say "compensated" I don't strictly mean money, which might not make sense if you haven't ever made something for free that a lot of people liked and gotten nothing but praise for it, but think of it like this: Say you run races and you get medals for doing it, except that the medals you get aren't made out of any valuable metals and one day you sort of ask yourself "why am I collecting these? are they even worthwhile?" and by doing this you kind of lose track of what you are doing. This is easily explained with the extrinsic versus intrinsic motivational theory of reward-based behaviors, but because of this it can be a somewhat easy art block to beat by sort of tricking your thought process into seeing other motivations in it. The only time it sucks badly is when you run into motivational hazards-- Like the prospect of thinking you might get your art stolen.
Like I said, I think there are probably a lot of different "art block" types out there, these are just the ones that usually get me. If anyone else has any "art blocks" of their own I'd like to know what they are, so I can try to either figure out ways around them or just maybe to think about as something I have not encountered myself before.
Updated by GameManiac