Mistakes, or careless at best? I'm thinking of a couple of scenarios I've had in personal vehicles, where I'm positive the design decision was the unreviewed work of some co-op student's summer project.
Case 1: Ford Taurus wagon, my wife calls in a panic because it's blowing all hot air, and the dash is awash in lights. I get her to shut it off, wait a bit, and limp the last few km home. Turns out the serpentine belt goes around a pulley, the center bolt of which is screwed into the engine block. When the bearing started to go, there was friction, and the belt spun the bolt out and it fell off. It could have been reverse threaded, like one pedal on every bike, ever. But no. If it had, the bearing would screech, we'd get it replaced, instead of just silently falling out with potentially catastrophic consequences.
Case 2: Chevy Venture van, where the lights on the rear door all stopped working. Turned out the wiring harness for them ran through this accordion hose at the top, plugged into the bottom of a rain gutter across the top. So as soon as that hose broke its seal with the trough, the whole harness is shorted.
Funny, I have never experienced this sort of stupidity in the Toyotas and Hondas that have followed these last couple American-branded vehicles.