Despite an explosion of research demonstrating the substantial health gains that can be made by shifting certain choices — in what we eat, in how (or whether) we exercise, in whether we smoke or follow through on medication regimes — progress on improving health-affecting behaviors has been less satisfactory than hoped for. In particular, there has been a frustrating gap between raising patients' awareness of the health risks certain behaviors carry and conveying such risks in a way that actually motivates a change in behavior. Too often, even when clinicians and other health educators provide clear, realistic, and repeated information about effective methods of risk reduction, people behave in ways that ignore or worsen those risks. Extensive communication campaigns about the risks of obesity, for instance, have done little to stem the tide of morbid obesity (Morrill and Chinn 2004). People often underreact to daily or cumulative threats, such as those of heart disease (Holtgrave et al. 1995; Hart 2005), even as they overreact to dramatic but less threatening events like the shortage of influenza vaccine (Slovic et al. 1990; Snowbeck 2004). And when a frightening event does occur, such as feeling a worrisome breast lump or chest pain that might signal a heart attack, people can become paralyzed by anxiety rather than seeking care (Schoenberg et al. 2003; Sanders 2003).