The Quote Illusion of a Tilted Horizon

Frederick may have been deceived by what's called the quote illusion of a tilted horizon. For us non-pilots, how can we understand this thing? Well, the way Paul and I were talking about it was with Microsoft Flight Simulator when we were kids. And if you imagine on that Cessna, he doesn't have a heads up display. He's got a window that he can see out of, and then he's got his instrumentation down below him or around him. Maybe he's not looking at that instrumentation that's letting him know how his plane is oriented. You may think you're flying level, you may be flying level and think you're not flying