How do you know how much you don't know?

I'd suggest there's a difference between "I don't understand how this is supposed to work" to "I do understand how this is supposed to work, and I don't understand why it isn't working."

Seat belt story seems to be Type 1. But what if a lot of "stupid" design decisions are actually Type 2?

And the reasons may or may not be good - somewhere on a scale from real budget and/or time constraints, lack of insight, indifference, penny pinching economics, to passive aggressive user hostility.

When Apple removed Magsafe no doubt there were perfectly good internal justifications for that decision. But ultimately the people outside the company who said it was a poor move from a user POV turned out to be right.