Esther Dyson writes in “Release 2.1, page 49″:

Here are a few basic principles for communities, based on my own experience both on- and offline:

• Each participant should be clear about what he is giving and what he hopes to get. Overall, those desires should mesh, although they may well be different for each individual. 

• There should be a way of determining who is in the community and who is outside it. Otherwise the community is meaningless. 

• Community members should feel that they have invested in the community, and that therefore it is tough for them to leave. The ultimate punishment in a strong community is banishment, expulsion, excommunication, excile. … All those words signify the terror of being cast out of the community.

• The community’s rules should be clear, and there should be recourse if they are broken.

Communities fail when these principles are not observed: for example [the] dance club where people are screened in or out by the bouncer may or may not be a valid community, depending on how well the bouncer knows the crowd and whether they know one another. On the other hand, a good bartender can create a wonderful community, as illustrated […] by Rick in the movie Casablanca.