I agree that some people just have very little ambition and determination. However, I think the statement "If they're not normal humans, it's only because they have more willpower than you." is way too overgeneralized given the limited information you have regarding jmnicolas' life (unless you know more than can be gleaned from his post here).

There are any number of completely valid reasons why a person would be too exhausted to work on a side project after work hours. People do have limitations. Some people have very difficult lives. People do burn out -- and everything does not boil down to having the willpower or not. I'm not saying willpower is irrelevant -- it is relevant. It just isn't the only variable in the equation.