I saw this quote in an advice column today, made to someone who was trying to set boundaries with her father. It seemed relevant to this conversation:

"Your dad does not have to understand. You don’t have to change his mind. The thing about having a boundary is not that you push and push and explain and explain until people say, 'I totally understand and respect that!' You just do what works for you and don’t debate it. He can be as disappointed as he wants, but the boundary is still there."