This study explores the influence of investor emotions on stock market performance, focusing on how cognitive biases and affective responses impact decision-making and portfolio outcomes. Drawing on behavioral finance theories, the research emphasizes emotions like fear, greed, regret, and overconfidence, identifying how these can lead to deviations from rational investment behavior. By analyzing empirical data and psychological frameworks, the study categorizes emotions into impulsive reactions and strategic misjudgments that contribute to common pitfalls such as excessive trading, loss aversion, and herding behavior. The findings reveal that emotional investors often underperform due to reactive strategies influenced by short-term market fluctuations, rather than long-term fundamentals. Moreover, demographic variables like age, gender, and experience level modulate emotional intensity and its effects on investment outcomes. The study recommends emotional regulation techniques, investor education, and AI-driven decision-support tools to mitigate irrational behavior and enhance performance. Ultimately, understanding the role of emotions provides crucial insights for both individual investors and financial advisors aiming to optimize risk management and returns in volatile markets.