Liking in Facebook (and on the wider web) is a modern manifestation of social proof that represents a specific piece of functionality that came from Facebook. This feature can be added to any website and allows people to add a like thus endorsing that particular content object. Figure 31-2 shows an example of how this is often used, note how the total number of people who have also liked an object is shown to reinforce its popularity (or unpopularity).
The following list summarizes the commercial motive behind applying the principle of social proof to your designs and how users are likely to respond to it.