Psychologists have shown we have only a limited amount of the stuff — and it’s drained quickly in situations where we need to make a lot of decisions. (Right. Like being a small business owner.) The good news is that we can actually train willpower. Like a muscle, willpower seems to become stronger with use, say neuroscientists Sandra Aamodt and Sam Wang, authors of Welcome to Your Child’s Brain. Even something as simple as using your non-dominant hand to brush your teeth for two weeks can increase willpower capacity, they say. Conquer that and you may be ready to stick to an exercise routine for 2017.