10K hours to develop expertise

Christopher Penn wrote about what it takes to become an expert, in response to a Daniel Levitin claim that it takes 10,000 hours to develop expertise.  Why you need 5 years at a job to be successful.

Consider this: in an economy when the average worker lasts about 2 years in any given job, how many workers have expertise? How many workers have achieved any degree of mastery? 1 in 4 workers at any given company has been there less than a year, according to Department of Labor statistics. 1 in 2 has been with their company less than 5 years.

Interesting thought.  Of course, it isn't just one job that builds expertise - it's the work one does, which Christopher acknowledges.

One element that Christopher also touches upon is the importance of the network of people I know and rely upon for advice, guidance and input.  That network grows and changes as I work.  And if I am changing jobs before that 10,000 hours clicks by, it is my larger world of work and the people who I interact with that help me describe my expertise.  Afterall, if no one thinks I am an expert, how do I establish the claim?