You don't have to be in recovery to appreciate the wisdom of this short prayer. The fact is, we don't have any control over some things, so whenever we try to control such a thing even in a small way, we are bound to be frustrated. It's no weakness to relinquish control; it's sanity. Rather, work on those things that you do have some control over, some "say" about in the situation.
We forget that the thing that we have the most control over is OURSELVES. Everything in this life is a choice: you can choose to set some things down because the battle is unwinnable or not worth the effort; you can choose to not let a situation throw you off your game; you can choose to involve yourself in a hope for change as long as you don't lay an expectation down as your goal.
Relinquishing expectations is the key to serenity. Hope, but don't expect.
And we have faith that our Higher Power has some purpose for us, some design in mind, and when we have no control, faith is trust that whatever should happen or needs to happen, will be what happens.