I think this is a universal feeling for every artist out there at every level. The trick is to channel the disappointment into improvement; there's an underlying cause behind what you make, something creating that feeling, and if you can identify even one of the things causing that then you've got something to try to work on. It helps to be specific in your self-critique, going "it's
all wrong" or "it's bad" isn't specific enough to be useful. As an example:
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I'd work on the wrap on the head so that the eyes actually look right, and I'd get more extreme with the hand and actually have it overlap the forearm so it's properly foreshortened (this is just straight on from the side; I didn't push the illusion at all which is an enormous struggle). It's helpful to itemize things like that, or try to think on a sketch later and prioritize whatever you can remember that bothered you.