It pretty much says that you can say the most craziest absurd thing ever and claim that people can't disprove it as long as you make enough excuses for it (ie: it's invisible! people haven't looked well enough for it! all traces of it were erased!). That's why usually the logical thing is trying to explain why X exists, not claiming it just does and challenging everyone else to prove you wrong.
Ive read that before. Thats like the flying spaghetti monster thing that smart alek middle school kids put as their religion on facebook. But, sometimes X does exist, or sometimes its better to believe X exists than to deny it. Believing in X sure makes a lot of people happy.