In the article Facts That Strain Personal Incredulity, Paul Krugman states:

But back to my main point: if you just can’t believe I’m saying the things I say, at least consider the possibility that you’re the one who just doesn’t get it.

I have always had another way of putting it that makes the same point.

If you can’t imagine something to be true, perhaps it is a problem of your lack of imagination.

Perhaps I ought to turn this into another one of Greenberg’s Laws.

Of course, what we should really be saying is,

If you could give me a few minutes to explain, then perhaps you could imagine it.