System calls that had user supplied memory structures for internal system use. What were they thinking?
Letting Jay Miner walk out. And the rest of the crew. All management stuff that though.
Not thinking of Moore's Law. Making the system a one-off and expecting to do something entirely different in the future. If it was a bad idea in 1983 I don't know, but at some point it should have been clear that you would be stuck with the basics and had to expand on them forever.