The central thesis of social capital theory is that ‘relationships matter’. The central idea is that ‘social networks are a valuable asset’. Interaction enables people to build communities, to commit themselves to each other, and to knit the social fabric. A sense of belonging and the concrete experience of social networks (and the relationships of trust and tolerance that can be involved) can, it is argued, bring great benefits to people.
Trust between individuals thus becomes trust between strangers and trust of a broad fabric of social institutions; ultimately, it becomes a shared set of values, virtues, and expectations within society as a whole. Without this interaction, on the other hand, trust decays; at a certain point, this decay begins to manifest itself in serious social problems… The concept of social capital contends that building or rebuilding community and trust requires face-to-face encounters. (Beem 1999: 20)
The above discussion is taken from this page: http://www.infed.org/biblio/social_capital.htm
See this fun YouTube video: http://www.youtube.com/watch?v=tTvbf1WVYFE