One of the major psychological foundations for the purported effectiveness of social media marketing is social proof.

What is Social Proof?

The idea is fairly simple: people are more likely to find a product or service appealing if there is evidence that other people find it desirable. Robert B. Cialdini, in his very popular Influence: Science and Practice, describes social proof as

an important means that people use to decide what to believe or how to act in a situation by looking at what other people are believing or doing.

We are social animals. Signals from our peers significantly influence whether we desire particular objects. In social networking, people put this principle into practice. They actively pursue “likes” or “+1s”. Consumers also actively seek visible evidence of engagement and approval for products and brands.