What was the mistake of H. Columbus?

Christopher Columbus sailed from the shores of the Old World to the west with only one goal, to reach the shores of India. During his life, he made four trips and in each of them he discovered new lands (Islands of the Caribbean Sea, the northern coast of South America). At that time, he did not understand that he had become the discoverer of a new continent, not yet known in Europe.

Until the end of his days, he did not doubt that the lands he discovered were part of India.