Everybody has to know when to quit. I would say you should quit when it´s no fun anymore or something you don´t enjoy anymore. Anyway before you quit you should ask yourself why you lost the joy. Maybe you get it back if you just go to your own roots or just lower your personal bar.
Did I seriously consider to quit? I don´t know, but I don´t think so. I always do some things beside amvs, that´s why I often need extra time to finish something. It´s good to get down a bit with gameing and other various things. It´s like DTJB said too: I have just too many ideas I want to see done before I can quit
I think somebody shouldn´t push himself too hard and should do other things beside this hobby too.




