[vannevar]

If I'd never applied myself, and thus never had success myself...

You're discounting the possibility of applying yourself and still not having success, which is really the whole point. Your argument is that those who fail will be more likely to blame luck, while Lewis' point is that those like you who succeed are more likely to overly credit their own effort. You're probably both right to some extent, but given that human physiological traits have a Gaussian distribution and wealth is distributed according to a power law, it would seem Lewis' view is closer to the truth.