there is an element of comic creation thats 'going with the flow' - i recently read about gerard way's experience with being a perfectionist and creating art, in which he said his comics are never finished when they come out, they just come out when they have to. sometimes you can only labour over something for so long.
that being said, theres also an element of 'straining' yourself - pushing, really. to create an interesting comic, you have to push yourself to develop creative images, pushing your abilities with perspective and posing and backgrounds.
personally, for me, it varies. sometimes im truly stuck on a pose ive challenged myself with, and its a struggle. other times it goes easy. it depends on what ive tasked myself with drawing, and what place im in. no matter what though, i just have to power on (even if powering on means not looking at it for 2 days)