A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.

I tell my friends that making software is like making M16s. You send them out of the factory, thinking you've designed the perfect gun, I mean how the hell do you use a gun wrong? Until you find out that a few people tried to use that top part to shoot arrows like a bow. What's even worse about software is sometimes they actually figure out how to use it as a bow and idiots start using M16s as bows and now you have to fix that because it's a horrible fucking bow.