Relatively little is known about why some patients are reluctant to engage in a collaborative discussion with physicians about their choices in health care. To explore this issue further, we conducted six focus-group sessions with forty-eight people in the San Francisco Bay Area. In the focus groups, we found that participants voiced a strong desire to engage in shared decision making about treatment options with their physicians. However, several obstacles inhibit those discussions. These include the fact that even relatively affluent and well-educated patients feel compelled to conform to socially sanctioned roles and defer to physicians during clinical consultations; that physicians can be authoritarian; and that the fear of being categorized as "difficult" prevents patients from participating more fully in their own health care. We argue that physicians may not be aware of a need to create a safe environment for open communication to facilitate shared decision making. Rigorous measures of patient engagement, and of the degree to which health care decisions truly reflect patient preferences, are needed to advance shared decision making in clinical practice.