Will power is temporarily zero sum

Unfortunately I can't spot the research this is based on, though the authors look like they ought to know what they're talking about. If it's right, there are interesting implications for education and coaching and similar endeavours. The article is this:Tighten Your Belt, Strengthen Your Mind - New York Times and we're told two basic things; "The brain has a limited capacity for self-regulation, so exerting willpower in one area often leads to backsliding in others. The good news, however, is that practice increases willpower capacity, so that in the long run, buying less now may improve our ability to achieve future goals"
So we need to strategise and work out either what we will focus on that will need our willpower, or what we might relax on to compensate for hard willpower work. But all the time building capacity. It would certainly explain why some people seem to have little impulse control: they've never learnt otherwise.