This essay delves into the complexities of managerial decision-making, examining the interplay between heuristics, biases, and overconfidence. It begins by defining overconfidence and its manifestations: overestimation, overprecision, and overplacement, providing examples to illustrate each concept. The essay then transitions to discuss heuristics as mental shortcuts, exploring their role in simplifying decision-making processes while acknowledging their potential to introduce cognitive biases. Specifically, it examines the availability, representativeness, and confirmation heuristics, providing examples to illustrate how each can lead to flawed judgments. The essay highlights the challenges of rational thinking posed by these biases and heuristics, emphasizing their impact on managerial effectiveness and the importance of recognizing and mitigating their effects. It draws on the works of Simon and other researchers to analyze the causes and consequences of these cognitive phenomena, offering insights into how managers can make more informed and effective decisions. The essay concludes by reinforcing the critical need to understand and address these cognitive biases to improve the quality of managerial decisions.