People who say no probably has a lot of trouble to get fit, get enough sleep -- sometimes NOT because they do not have the resources, but because they are not happy. They hate life, so why makes it better? I have observed this in myself so I wonder whether it is universally true.
I have observed that whenever I have a clear target in my life (e.g. I need to pursue this girl I like, or, I need to figure out Linux 1.0 VFS and I have a clear path before me), I immediately take care to do exercises, eat more healthy food, and try to get good sleep -- but if I cannot find an objective, or I have lost interests and are in the middle of finding a new one, I find myself a lot more obnoxious, and sometimes I "proactively" destroy my health because I don't care about it. Unfortunately I rarely find a clear path before me so the later status is more or less permanent while the former one is rare, maybe once per year -- but when I reach the first status it usually grabbed me for 2-3 months.
Mental stability is probably one of the reasons different people have vastly different productivity or achievements. It is mental stability that brings focus, not the other way around.