Personally I believe that the myth of the 10x engineer comes from the very real and very visible fact that often times, one engineer will be 10x as productive as someone sitting in the next desk over. Why is this? There are numerous factors, and certainly innate skill and programming practice come into play. But I think that only gets you to, at maximum, 2x the average. To get to the perceived "10x" you need luck, the right mindset, and a the buy-in from management to push others aside and take on the most juicy projects (which is self-reinforcing once management sees you as a "10x engineer"). "Stealing the Corner Office" is a good book on such tactics (although it ostensibly applies to middle-managers).