We develop a behavioral‐decision model to highlight entrepreneurs’ decision making behind venture opportunism. We find that opportunism can present to entrepreneurs and their new ventures a risky yet beneficial choice to secure short‐term gains at potential social costs. We posit that, motivated by loss aversion, entrepreneurs may accept the risk and engage in opportunism when their ventures confront economic losses. For instance, a high risk of venture failure may motivate entrepreneurs to act opportunistically in the hope that the failure can be averted. We further posit that such loss‐averse decisions will be moderated by the entrepreneurs’ personal bonds to their new ventures. That is, the scale of entrepreneurs’ personal investment in their ventures will intensify their economic loss aversion posed by venture failure risk. In contrast, when entrepreneurs use their personal social capital to support their ventures, they will personally bear more of the down‐side risks of opportunistic behavior and thus be less likely to act opportunistically to countervail a potential economic loss. Results based on the data collected from 244 NEEQ‐listed new ventures in Beijing and Tianjin in China support our predictions.