Oh man...honestly, there's so much nuances to giving an actually useful critique, but also how we see our own art is completely different from how other people see it. So maybe this detail you just realized was really bad, other people didn't see as terrible either, or they thought something else is wrong.
Also there may be a chance you're just not on the level to notice the problem and make changes, or you just so used to something it will be painfully hard for you to admit the problem. Like if someone will say my characters' legs are too short or their faces are crooked to the left, I can only laugh in their face because yeah, I know.
(Also I just know from myself that some people can be in the mood where anything can throw them into artblock or something and I won't be good snapping that last straw)
Well, on the other hand maybe that's why it takes me so many years to learn what others learn in a few months