Predicting the survival of terminal cancer patients is a difficult task. To better understand this difficulty, we divide prognostication into two distinct elements: foreseeing and foretelling. Foreseeing is a physician's silent cognitive estimate about a patient's illness. Foretelling is the physician's communication of that prediction to the patient or significant others. In this article, we review the impact of each element of prognosis on physicians' overall prognostic accuracy. We show that physicians often make unwitting, large, and generally optimistic errors in foreseeing patients' prognoses. They also may make more conscious, but equally large, optimistic errors in foretelling prognoses to patients. The net effect is that patients may become twice removed from the truth about their illness, both times toward a falsely optimistic prognosis. We also describe the possible consequences of these optimistic prognostic errors. Finally, we review techniques that may improve physicians' prognostic accuracy. We conclude that part of the challenge of providing humane, compassionate end-of-life care to cancer patients may involve accurately foreseeing and foretelling their prognoses.