The authors of this paper conclude that the qualities which make things like diseases into epidemics are actually the opposite of the qualities that make social and peer-related ideas into phenomena. An epidemic spreads widely if people travel long distances and infect new people, in essence, if they have a high number of interactions and contact with others. An idea can actually spread better with fewer interactions and contacts; the more friends you have, the less likely any one idea will become popular among all of them, thus influencing your opinions strongly.