From the book 'Peak: Secrets of the new science of expertise', Anders Ericsson and Robert Pool state that to be an expert you must be successful at something more than once.

Which means that just because someone was successful doesn't mean they were directly responsible for it. Like being on a team where you may have even been the manager but the team players were what made it truly successful. If you were successful on two different teams then the odds of you being a key player in that success are much higher.