In Outliers, Gladwell does not explicitly say what is overvalued in common sense explanations of sports greatness. However, we can infer what he thinks is overvalued. This can be found in Chapter 1. Gladwell starts Chapter 1 by talking about the 2007 Memorial Cup hockey championships in Canada (for the highest level of junior hockey teams). Gladwell says (I cannot give a page number because I only have this book on Kindle) that people believe that hockey (and all sports) is a meritocracy. He says that
Players are judged on their own performance … and on the basis of their ability, not on some other arbitrary fact.
This is the common sense view of greatness in sports. Players are not judged on the basis of how rich their families are or how popular they were in school. Instead, they are judged only on their own performance. But Gladwell goes on to ask “Or are they?” By doing this, he is implying that this is not really how players are selected for greatness.
Gladwell goes on to explain that hockey players who become great tend to be born early in the year. They are closest to the cutoff date for playing in a given age group in junior hockey. Therefore, they are the oldest on their teams. This means they are (on average) bigger and stronger than kids born later in the year. This makes them look better early on. Because they look better, they get more coaching, gain more confidence, and generally progress more than those born later in the year.
What Gladwell is telling us, then, is that players’ own merit is overvalued. Players don’t just become great because they have talent and determination. They also become great because their birthdates give them an advantage.