people need to hear a new idea multiple times before making a change.
(人们在作出改变前需要重复听到一个新观点很多次)
A disease, Centola suggests, can spread as a simple contagion, but behavior that can prevent the disease — such as going to a clinic for a vaccination — might spread only as a complex contagion, thus needing to be spurred by reinforcement from multiple neighbors in a social network.