What makes someone an expert?

There has been a lot of talk over the past 24 hours about who is an expert in the domain industry. What makes someone an expert? There are obviously no set rules or definitions. Some will say if you have no verifiable public domain name sales you are not an expert. But there are private people who possess great expertise that are not a part of the day to day community. And just because you got lucky and sold a few names that does not necessarily make ...