Why does entrepreneurship training work? We argue that the feedback loop of the opportunity development process is a training element that can explain the effectiveness of entrepreneurship training. Building on action regulation theory, we model the feedback loop as a recursive cycle of changes in the business opportunity, goals, performance outcomes, and feedback. Furthermore, we hypothesize that error orientation and monitoring can strengthen or weaken the cycle, and that going through the feedback loop during training explains short- and long-term training outcomes. To test our hypotheses, we collected data before, during, and after an entrepreneurship training program. Results support our hypotheses, suggesting that the feedback loop of the opportunity development process is a concept that can explain why entrepreneurship training is effective.