The acceptance-- if it is sincere and without strings-- can have a magical effect on things.
If partner A is trying to get partner B to do something or be a certain way, partner B tends to see the issue as A's "problem." There's a triangle: A, B, and The Problem.
But when A sets down the problem by the side of the road and says "it is no longer my problem, I'm fine with things the way they are," then all of a sudden the there is no more triangle. B is alone with The Problem. That can cause real panic and be a much greater motivation for change than when the sitch was a triangle.
This is IF B secretly or publicly recognizes that The Problem is in fact a problem. Which chances are B does if B has been arguing about it and resisting it for years.