That position or opinion you think no one can possibly hold? That one where you think they must be lying, or doing it for status points, or mistaken, or just plain evil? They really, honestly do believe that. Their personal, internal experience is so different from yours that the "impossible to honestly believe" belief is just straightforwardly true inside their heads. This doesn't make their beliefs true, right, or moral, but they do really believe it. Consider what sorts of things would make someone believe it as a way to better understand them. In other words, (side that seems laughably wrong) aren't just evil versions of (side you're on). They really do start from different foundational beliefs than you.