In reply to David New.

Absolutely. There are many psychological factors involved.

Again I emphasize that this is not an attempt to model the spread of a disease nor to model how attitudes and preconceptions affect how people act. As you say, a model like that would surely incorporate age, education status, gender, and many other variables. My goal is just to point out a simple mathematical fact: Even when you strip away all the complications that are involved in a realistic model, you still see that the public-health recommendations apply. Namely, to reduce the cumulative probability of an event, you should reduce the number of interactions (stay at home; social distancing) and reduce the probability of the event (wash hands; wear masks). These factors are the mathematical "core" to reducing the spread, which is why we hear so much about their importance.