Biases continue to be an important aspect of human judgment and decision making because they can lead to unfavorable outcomes. Optimism bias is one type of bias that is often overlooked because of its association with good health and positive outcomes. However, the existence of optimism bias in human judgment can be very damaging especially when it distorts a person's view of future events. In order to better understand optimism bias we explore the benefits and downsides of optimism as well as some empirically-based origins of both optimism and pessimism. This provides a backdrop for a methodology for quantifying optimism and pessimism using the Brier score developed for calibrating weather reporters and a discussion about how sports bookies make well-calibrated decisions. Results are explored from an optimism survey given to a cohort of eighty systems engineers, which ultimately portray the degree to which optimism bias influences decision making in large projects. Further exploration of the key differences in optimism across professions helps distinguish motivational factors and characteristics of well-calibrated professions. We also present results from a calibration exercise, designed to infer if such activities can be adopted to assist systems engineering estimation. Finally, we provide prescriptive advice on how individual decision makers can better manage their optimism and become more realistic. 2009 by Ricardo Valerdi & Craig Blackburn.