"In situations like this you have to help people figure out for themselves where their own internal model is flaky. Sometimes that takes a while."

If you are any good at this, please write a book. I would pay a handsome some for even just incremental improvement in this skill.

My day is filled with people going around acting as if 2 + 2 = 5. Thus far my only strategy is to say, "Are you sure it's 5? I'm pretty sure it's 4." Repeat over and over for years until people adopt the new "2 + 2 = 4" mental model and forget I'd been saying it for years...