I think he meant the mindset in general, not exactly the strict meaning or interpretation of the words "below average". I think he meant tackling each problem

I think he meant the mindset in general, not exactly the strict meaning or interpretation of the words "below average". I think he meant tackling each problem by assuming that you're below the average and therefore examining and solving it more thoughtfully and carefully than you would if you just knew you're so damn good you don't really have to pay much attention to it. So, how I saw it, it's about emphasizing that you're not quite sure how to solve a problem and, in this, thinking everyone else does makes it easier to remember the meticulousness that you desire.