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

More from Mostly Harmless

• All you really need to know for the moment is that the universe is a lot more complicated than you might think, even if you start from a position of thinking it's pretty damn complicated in the first place.
• Besides, she told herself, taking a deep breath, if life had taught her anything it was this: Never go back for your bag.
• "Don't tell me about the future," said Ford. "I've been all over the future. Spend half my time there. It's the same as anywhere else. Anywhen else. Whatever. Just the same old stuff in faster cars and smellier air."
• Everything you see or hear or experience in any way at all is specific to you. You create a universe by perceiving it, so everything in the universe you perceive is specific to you.
• He always entered via the ventilation system rather than the main lobby because the main lobby was patrolled by robots whose job it was to quiz incoming employees about their expense accounts.
• He had a very simple method of dealing with establishments of which he was not a member. He simply swept in as soon as the door was opened, pointed back at Arthur and said, “It’s OK, he’s with me.”