Human behavior often seems “maladaptive”, “self-defeating”, or “dysfunctional” to the observer. Upon closer examination, the rationality of human behavior largely depends on the temporal frame adopted; behaviors judged to be maladaptive in the long-run are usually driven by a strongly favorable balance of immediate costs and benefits. That is, many ‘‘maladaptive’’ behaviors are associated with substantial long-term costs and few (if any) long-term benefits; however, these same behaviors are frequently associated with many benefits and few costs for the individual at the time of action. In contrast, many avoided behaviors that seem ‘‘adaptive’’ to the outside observer, are in fact associated with substantial costs (and few benefits) at the time of action, leading to the perplexing but common state of affairs where individuals know ‘‘what is good for them’’, but do not do it. We present a new theoretical framework—Temporal Self-Regulation Theory—as a way of understanding human behavior in general, and those special instances of seemingly ‘‘self-defeating’’ behavior that have important implications for physical health. This theoretical framework incorporates thinking about temporal aspects of behavioral contingencies and the biological roots of self-regulation to make sense of human behavioral patterns that seem to represent, on the surface, significant deviations from rationality.