This study investigated the relationships among the psychological characteristics and personality factors of individual investors, the characteristics of their stock investment behavior, and stock investment returns. The purpose of the research was to identify the circumstances under which individual investors make erroneous investment decisions, to find the decision-making errors that cause such mistakes, and to analyze whether these errors are attributable to personality variables. Rather than establishing and testing specific research hypotheses about the relationships among individual personality, investment behavior, and investment performance, this study presented the characteristics and performance of individual investors through an exploratory interdisciplinary approach. The results of this study are as follows. First, consistent with prior research in behavioral finance, investment returns decreased as individual trading frequency increased. Second, returns also declined as confidence in one's own investment ability increased. These results suggest that overconfidence induces excessive trading, which in turn leads to lower returns. Finally, among personality factors, extraversion was found to cause excessive trading and consequently reduce returns.