I think he's intentionally focusing on the luck aspect because I think his audience (Princeton undergrads) is used to the first narrative. As sort of an outsider (I'm a graduate student here), I sometimes get the sense that a fair amount of undergrads here are a bit too self-important. Certainly there are many awesome, down-to-earth people here too, but there are also a lot of people who are caught up in the fact that they are Princeton students and that by itself perhaps makes them better than students of "lesser" schools. I think in particular, Lewis' last full paragraph should be the take away for these students. Yes, they are very gifted and they may deserve every bit of benefit that comes their way, but they should also remember that there is at least some part of that they didn't/can't control. Acknowledging and being humbled by that will go a long way in life.