Well, the average Joe by definition will not be and will not aspire to be a top performer in any field, which is kind of what the book is about.
But what the average Joe will benefit greatly from is this point that trying out several career paths before committing to any one in particular is how you find the job that truly fits your skillset and personality. In turn, you will not only be a million times happier but also probably better at your job. I really didn't focus on this point but the author did. Great comment