Research suggests that overconfident managers often harm firm value by taking excessive risks due to overly optimistic future outlooks or inflated self-assessments (Griffin and Tversky, 1992; Malmendier and Tate, 2008). Overconfident CEOs are reported to overestimate the expected returns from uncertain ventures. However, Hirshleifer, Low, and Teoh (2012) present evidence that overconfident CEOs, who tend to be more enthusiastic about challenging and risky projects, invest more in innovation and often succeed, introducing the "overconfident manager puzzle" where such managers enhance rather than damage firm value. This study aims to test these conflicting findings in the context of Korean firms. It explores the hypothesis that optimistic managers—unlike overconfidence, which is traditionally viewed as harming firm value through overinvestment—might instead be innovators who enhance firm value. The study utilizes a novel methodology involving machine learning to measure managerial overconfidence. Unlike U.S. studies that often use stock options as indicators, this research leverages text analysis of managerial opinions disclosed in business reports, using the BERT machine learning model to quantify optimism. The ambiguity in measuring overconfidence in previous studies is another consideration. Psychologically, overconfidence is seen as an irrational bias, but empirical variables might capture a manager's rational optimism about the future. If a manager's outlook is rational, overconfidence could lead to positive outcomes, unlike the negative connotations typically associated with it. Many studies interchange overconfidence with optimism, where the former implies irrational excessive confidence and the latter signifies a positive future outlook. Generally, overconfident CEOs are believed to make poor decisions by overestimating future performance and underestimating risks, leading to value-destroying mergers and acquisitions (Malmendier and Tate, 2005, 2008). Such CEOs are often reported to overpay in M&A deals, necessitating strict control through compensation and governance structures. Overconfident managers also tend to invest more than their less confident counterparts, potentially harming firm value through overinvestment (Moez and Amina, 2008; Chen, Ho, and Ho, 2014). Conversely, some researchers highlight the positive roles of overconfidence. It can enhance decision-making execution, encourage necessary risk-taking for shareholder benefit, and stimulate entrepreneurial activities (Russo and Schoemaker, 1992; Goel and Thaker, 2008; Bernardo and Welch, 2001). Hirshleifer et al. (2012) found that overconfidence negatively impacts acquisitions but positively influences innovation. They suggest that overconfident managers in firms with innovation opportunities can achieve significant success, unlike those in firms without such opportunities who might make detrimental acquisition decisions. The study's empirical analysis yielded several key findings. First, contrary to expectations, there was a negative relationship between CEO Optimism and risk, as measured by stock return volatility, suggesting that optimistic CEOs do not prefer riskier projects unlike overconfident CEOs. However, this relationship turned positive when controlling for capital availability, indicating that optimistic CEOs choose risky projects when capital is accessible. This implies that the measure of optimism might reflect rational optimism rather than irrational bias. Second, optimistic CEOs were found to increase R&D investments and engage more in innovation activities, such as filing patents. Third, they tend to hold more cash to seize future investment opportunities. Last, optimistic CEOs were confirmed to enhance firm value, aligning with Hirshleifer et al. (2012), suggesting that they are rational optimists driving innovation rather than irrationally overconfident leaders. In conclusion, the study reaffirms that optimistic managers can be seen as rational optimists whose confidence drives innovation and firm value enhancement, challenging the traditional view of overconfidence as purely detrimental.