I know that is a tenet of this board, but I do not fully subscribe to it either. In a strict sense I agree that I cannot cause someone to change, but I can create conditions in which the other person might reevaluate their choices. Changing the reward/consequence balance is one example. The other person still does not have to change, but s/he might get mighty uncomfortable. Combine this with my other tenet that most people take the easy way out, even if it takes some time for them to come around, and you DO have the ability to effect change. It just might take some time. Only the most stubborn will endure hardship for years and not change.
Boundaries do this exact thing. If a boundary did not exist before, but I decide to put one up, if for no other reason than a whim (or I suddenly have an epiphany and realize I need this boundary), then I am doing so to tilt the odds in favor of some sort of change. That may not be direct manipulation, but to the person on the other end, I am not sure if it makes much difference. It feels like manipulation to them. It is an exertion of power. There is an obstacle blocking their easy path that was not there before, and I consciously put it there. To me, that would feel like manipulation and control. IMO, this is all a matter of semantics.
