So your pair is proposing a route or plan that you don't agree on. Am talking about a refactoring, a redesign or just the way to test drive the next feature. You have told him your reasons no to agree with him and there is no way to get to an agreement. It's perhaps frustrating because you believe his strategy will fail but he definitely wants to proceed that way. What do you do? Argue forever?
I don't think you have to always agree on the path you are going to walk. The important thing is that both understand the plan so that driver and navigator can help each other get there. In those situations I end up saying... I believe this approach is not the best and I would try out something else - something I explained already... but anyway, I'll help you with your idea, let's do it.
Several times my pairs have proven that they were right and the plan was effective. Some other times it wasn't a good idea, but we built a trustworthy relationship, a supportive one.