We have a client that was struggling to get members to join.
It's a private, inception-stage, community. The concept seems good and well-researched. Existing relationships have been established with many members of the target audience.
However, the recipients weren't responding to the invitations to join. The e-mails were opened, but the links weren't clicked.
There are two interesting things here. First, with the data we have now it's incredibly easy to diagnose exactly what the issue is. If you look deep enough you can determine, specifically, why the intended action isn't taking place. Second, the tiny details make a huge difference.
We're programmed to ignore the majority of e-mails. Any e-mail that appears to contain a marketing message, is too long, has the wrong few words initially, is too formal (e.g. dear -vs- hi), lacks personality or personalization, contains the wrong subject line, originates from a corporate account, or has the wrong structure isn't going to get a response.
There is a danger here. Instead of realizing the tiny details are the problem, you can conclude that there is a major issue with the community concept.