The onset of epidemics is significantly influenced by external circumstances, often stemming from minor changes. A notable example can be found in New York City during the mid-1990s when crime rates soared. The authorities attributed this rise to seemingly inconsequential details such as graffiti-covered subway cars and unchecked subway-fare evasion, which signaled a lack of concern for the deteriorating situation, giving the impression that anything goes.

To combat this crime epidemic, the authorities began paying attention to these minor details. Graffiti was swiftly removed, and fare-evasion was made a punishable offense. By demonstrating zero tolerance for what appeared as trivial matters, the message was clear: reckless behavior was no longer acceptable. Over the following years, the crime rate decreased rapidly, and the epidemic was reversed through these minor interventions.

Another subtle factor contributing to the emergence of social epidemics is the size of a group. The “Rule of 150” posits that dynamic developments that extend beyond the group only occur in gatherings of no more than 150 people. In simpler terms, if you want clubs, communities, companies, or schools to incubate contagious messages, keeping them small is crucial. Even the slightest changes in a context can determine whether an epidemic gains momentum.