Why did Columbus choose to embark on his 1492 voyage and what was his great error?

Columbus embarked on his 1492 voyage primarily to find a westward route to Asia in search of lucrative trade opportunities, particularly for spices and gold. His great error was underestimating the Earth's size and miscalculating the distance to Asia, leading him to mistakenly believe he had reached the East Indies when he actually landed in the Bahamas. This misjudgment not only altered the course of exploration but also set the stage for European colonization of the Americas.