Just because it might be a trope, doesn't mean there's no truth to it. I'm not particularly large. But some guys have had trouble either on insertion of my cock or after I've pounded them for a while. And I'll admit, I'm no bottom, so I don't have personal experience. But I can't see any way that Castro wouldn't cause at the very least some minor pain or discomfort at somewhere in the process for the average person whether it's on insertion, during the old in-and-out, the dismount, or the day after.