This study aims to identify and explain bidders' irrational and uneconomical behavior in internet auctions and its causes by introducing the concept of escalation of commitment from Staw (1981), which has been frequently applied in psychology and organizational behavior theory, to explain the irrational and uneconomical bidding behavior that can emerge in the internet auction process. To this end, the factors that bidders consider important in internet auctions were identified through a review of existing theories and research, and product involvement, perceived price fairness, and bidding effort were proposed. In relation to escalation of commitment, psychological sunk costs, self-justification, and completion effect were presented as influencing variables. The empirical analysis results showed that higher levels of product involvement and perceived price fairness lead to greater bidding effort. Additionally, it was confirmed that increased bidding effort has a positive effect on psychological sunk costs and self-justification, and that the completion effect has a moderating influence on these relationships. Furthermore, higher levels of psychological sunk costs and self-justification were found to have a strong effect on the willingness to continue bidding.