It should provide value for individual users (Virality)

2006.05.02 - Bokardo - The Del.icio.us Lesson: Personal value precedes network value.

The one major idea behind the Del.icio.us Lesson is that personal value precedes network value. What this means is that if we are to build networks of value, then each person on the network needs to find value for themselves before they can contribute value to the network. In the case of Del.icio.us, people find value saving their personal bookmarks first and foremost. All other usage is secondary.

2012.06.12 - Chris Dixon (a16z) - Designing products for single and multiplayer modes

2015.01.31 - Chris Dixon (a16z) - Come for the tool, stay for the network