Comment by dang

That's a property of human beings in general. It's also a nice example of how sometimes a conundrum goes away when you make it more general.

That is, it seems incredible (going back to the GP) that engineers assume they understand economics when they don't. It's somewhat less incredible (applying your formulation) that engineers assume they understand things they don't. While it may still be incredible that engineers are so assumey, at least we no longer need to marvel at their assuminess about economics.

If we go one more step and state it as everyone assuming they understand things they don't, it's no longer incredible at all. What would be incredible is if anyone didn't.