The notion of determinism vs. free will, and the notion of self-acceptance vs. striving for virtue, are parallel notions. In the one, tho it seems that cause & effect operate in life to the exclusion of chance, such that absolutely all things seem to proceed from physical causes, still that causation remains overwhelmingly invisible to our eyes (lacking, as we do, the omniscience & sheer cognitive power often attributed to God). In this case, one still operates in & as a self by which choices are made & carried out. Even if whatever we do is by a kind of unseen compulsion, and not by truly free choice, still the appearance is of a kind of free choice, and it is what we operate with (the use of appearances). Even if some hard determinism underlies all life (God, chaos, the unnameable), free choice is the only way that we, as people, can manage our movements to or from, and so sort out our impulses.
To the extent that a man’s hand is real, & setting aside death and violence, then to that extent he may use his hand as he chooses.
So also with self-acceptance. If you decide you are inadequate, or choose to believe so, that judgment will result either in self-castigation to no useful purpose or (at the other extreme) to spurring oneself on to improvement & accomplishment. If you simply ignore judgment (the notion of better or worse) and say to yourself,
“I’m my self and that’s all; nothing will change who I am, so it’s unreasonable that I should try to be that which by nature I am not,”
then you are abdicating self-guidance, abdicating the ruling faculty, even abdicating oikeioosis (self-interest), the fundamental rule of dynamic nature. It may be that you can never truly & fundamentally change who and how you are, but at least you can learn and improve and often – in many cases – excel in relation to your original self or others.
To refuse to accept your condition, your essential given – whether a world of causes you have no control over, or a self you cannot exchange for another – is in either case to condemn yourself to despair or self-hatred. To simply and passively accept conditions is, however, to abdicate what little freedom you can exercise and diminish yourself altogether. The untidy answer is to do both – accept the world or yourself as the starting point (“warts and all”) and then proceed towards the Good therefrom.