Acceptance isn't passivity or surrender, but an active engagement in reality, in real time, on its terms. As such, acceptance is realism, a seeing of reality as is, which, of course, requires existential courage rather than an escapist, idealistic flight into what should be.
Accepting the reality as it is now means just that: accepting the reality as it is now! If you don't like the way reality is right now, change the future - but you first have to accept the present.
You might think: "If I am to accept that at any given time I am doing the best that I can, then how am I to achieve my goals? How am I to improve myself?" The false choice here is this: either accept or change. Acceptance of the fact that at any given time you are doing your practical (not theoretical) best doesn't mean that you cannot try to improve the next moment. Of course, you can.
Accept and change: accept that at any given moment you are doing the best you can do and, having learned from the experience of this given moment, try to change and improve the next moment to the extent that you can. Automatic, reflexive, on-the-fly perfectionistic rejection of reality as not being good enough triggers a mindless rush to improve it.
Acceptance, that begins with the acknowledgment of what is as being the best that it can be at the given moment, is the beginning of mindful change.