Have you ever told a friend or client that s/he could wire up the PC and external devices all alone because plugs only fit into 1 specific socket and cannot be mixed up? And if there is more than 1 socket of the same type they are color coded (like for PS/2 and audio sockets)? — I did, but I won't do it again, probably, at least not if I have to assume that a standard USB wire of type A-B is around!
I thought I had seen it all, like one guy who plugged in a 15-pin VGA wire upside-down. In former times, every sysadmin knew to warn people that phone wires with smaller RJ plugs do fit perfectly into RJ45, and in fact can cause great damage. Fortunately, these wires are pretty much extinct nowadays. I really thought it was safe to let users do the wiring.
Today, a friend of mine called me because he couldn't install his new printer. The printer offered LAN and USB. My friend made sure the printer works by itself but when connected to a PC via USB the PC did not find any printer.
Well, of course not! I had no idea how damn well a Type B USB plug fits into a RJ45. Besides, I don't want to know how much damage it can cause. It short-circuits at least 6 pins! However, for my friends sake I'll now go and check it out.