Now...everything we do that requires will-power throughout the day represents a withdrawl from our account. Make the bed? $10. Say "no" to desert? $15. The amounts we need to withdrawl for an action depend of course on the person (my act of will-power could be your act of enjoyment) and so does the starting balance of our accounts - some people are just built with more mental discipline than others (and according to this theory, there's really not much we can do about it). When we've finally blown through all our will-power cash account, we're just victims of our whims for the rest of the day, or so the theory goes.
Our goal, then, is to spend our will-power as wisely as we can throughout the day. For many of us, we can distribute our will-power wealth equitably across different facets of our life (health, family, work, etc.), but for those in fields of extreme mental rigor, they just can't afford it. If you're working through an intricate argument on Kant's metaphysics...or creating the Linux kernal, you need every last ounce of your mental discipline for your work - you literally nothing left over for shaving, combing hair, checking whether socks match, and generally making sure people don't mistake you for the homeless. This, then, maybe explains why our great programmers, philosophers, and physicists look so unkempt. They have channelled all their mental energy into their work, with none to spare.
Who knows if this theory is correct, but I love to use this at home with my wife anyway. Her: "Take out the garbage"? Me: "Nope, sorry, solved a really tough ClassLoader problem today." (and no, this has never worked for me)
But if it does have any merit (and I think it has some), then it means that it's a software company's duty to attend to any environmental, organizational, or ergonomic factors that suck will-power from its developers, so they can instead maximize it on things that help the business (like writing code!). Does this happen in practice? Not really. In some companies, it's possible for a developer to blow through their whole will-power account by noon with constant interuptions, endless meetings, slow machines, etc. This, of course, is the whole premise of Peopleware...