I realize this doesn’t exactly contradict you, but even if true (and it probably is/was) I think those “most” would not in fact think of difficulty but rather of how well you need to solve the problem. That is, a bathroom-cleaning robot that misplaces the shampoo five percent of the time might be considered “solved problem”, but a self-driving car that “misplaces” the car even one percent of the time would sound very scary. I think it’s the difference in “acceptance criteria” that makes people misrank tasks rather than relative difficulty.