People tend to overestimate the likelihood of positive events. Being a member of Group B does give them a chance of getting a lucky meeting with some Group A luminary who can radically change their life. The problem is, there's a 0.1% chance of that, but they've thought about it enough and fantasized about it enough that they think their odds are considerably better - they think that by going to TED they've got a real shot at their dreams coming true.