Can some heroic math-savvy LWer compile a poll about 'the most difficult kind of math I had to learn in high school' and 'in uni'? A separate issue would be 'probable reasons for failure', a multi-choice question (please include 'well-meaning family help'). And somewhere there'd have to be an option 'never experienced this KoM before'. This way we'll get some data about what we struggle(d) with. Also we can do it for 'the clicking' KoM. ... Actually, perhaps it can be better done as a survey, with an additional option allowing people to state the 'interconnectedness' of KoM they find intuitive. As in, I found matrices completely separate from all preceding topics... And then, we can compare the clouds of 'successful' math learners with those of 'unsuccessful' ones, and [under the assumption of similarly built courses] find out what links fail more often.