Why did Christopher Columbus continue to believe that he had reached Asia?

Christopher Columbus maintained the belief that he had reached Asia primarily due to significant miscalculations regarding the Earth's geography and a reliance on inaccurate historical sources.12

His conviction was rooted in several key errors:

• Distance Miscalculations: Columbus underestimated the distance between Europe and Cathay by using an incorrect length for a degree of latitude. By substituting the shorter Italian mile for the standard measurement, he drastically reduced the perceived distance across the Atlantic.12
• Reliance on Classical and Medieval Sources: He favored the geographical estimates of Ptolemy and Marinus of Tyre, which exaggerated the east-west extent of Asia. Furthermore, he incorporated the accounts of Marco Polo, which suggested that the lands of the East, including the island of Cipango, extended far into the ocean.12
• Confirmation Bias: Columbus interpreted his findings through the lens of these expectations. When he encountered Caribbean islands, he convinced himself they were part of the Asian mainland or nearby archipelagos, even forcing his crew to swear that Cuba was the coast of Asia.32