Social proof is the psychological and social phenomenon that people will follow the actions of others if they believe the crowd is making the right choice. For example, if someone is looking for a new laptop, they may begin with online reviews from Amazon users, look up reputable laptop review sites, and draw their conclusions from the experiences of others.
According to a paper by Duncan Watts and colleagues entitled: "Everyone's an influencer", the most common risk in viral marketing is that of the influencer not passing on the message, which can lead to the failure of the viral marketing campaign. A second risk is that the influencer modifies the content of the message. A third risk is that influencers pass on the wrong message. This can result from a misunderstanding or as a deliberate move.