Clinical and surgical decision-making is significantly influenced by the mechanisms described in dual-process theory of thinking. System 1, which is fast and intuitive, enables efficient responses but introduces cognitive vulnerabilities that can distort diagnosis and therapeutic choices. System 2, more analytical and deliberative, serves as a reflective counterbalance, although it does not always succeed in correcting initial conclusions. This chapter examines how these systems interact in real clinical settings and how the resulting biases affect both diagnostic accuracy and patient safety. Particularly relevant biases in medical practice, such as availability, overconfidence, confirmation, and anchoring, are reviewed, and findings demonstrating their direct impact on surgical decisions and multidisciplinary team meetings are analyzed. Additionally, factors that exacerbate these biases, including stress, hierarchical pressure, and the emotional burden inherent to surgical practice, are discussed. Finally, the importance of awareness, metacognition, and explicit education about cognitive errors is addressed as strategies to mitigate their detrimental effects and promote safer, more effective clinical reasoning.