This paper uses proprietary data from a blackjack table in Las Vegas to analyze how the expectation of regret affects peoples' decisions during gambles. Even among a group of people who choose to participate in a risk-taking activity, we find strong evidence of an economically significant omission bias: 80\% of the mistakes at the table are caused by playing too conservatively, resulting in substantial monetary losses. This behavior is equally prevalent among large-stakes gamblers and does not change in the face of more complicated strategic decisions.
