Acceptance is absolutely the best tool in my recovery tool box. It means seeing things as they really ARE, not the way I'd like them to be or how I'm afraid that they might be.
One of my favorite quotes in the AA Big Book comes from a personal story (now entitled "Acceptance Was the Answer"):
And acceptance is the answer to all my problems today. When I am disturbed, it is because I find some person, place, thing or situation -- some fact of my life -- unacceptable to me, and I can find no serenity until I accept that person, place, thing or situation as being exactly the way it is supposed to be at this moment. Nothing, absolutely nothing happens in God's world by mistake. Until I could accept my alcoholism, I could not stay sober; unless I accept life completely on life's terms, I cannot be happy. I need to concentrate not so much on what needs to be changed in the world as on what needs to be changed in me and in my attitudes.
(Can't cite to the 1st Edition, it isn't in the 1st Edition.)
You don't have to be an alcoholic for that to be true. I believe it is true for every human being on the planet.