Despite three more voyages, the Genoese explorer sailed over life's horizon convinced that he had discovered a way to the Far East by travelling west across the Atlantic. He had gone in search of the treasured spices and silks of India and China. Muslim states had blockaded the overland route and Europe was getting desperate. The Portuguese decided to find a way through by sailing east around Africa.
Columbus went off on the opposite tack. His blunder - if pioneering a trade route to America can be called that - was the result of some fundamental errors in his calculations, errors known to other sailors and Columbus's potential sponsors. Most sailors and explorers accepted by then that the Earth was round. And most experts agreed with the Greek astronomer Ptolemy regarding how much of the surface was land and how much was water. However Columbus preferred the calculations of Marinus of Tyre, a geographer and mathematician, which resulted in much less ocean. He added in a mistake regarding degrees of longitude and also misread the maps, believing that the distances were in short Italian miles of 1,238m, not the longer Arabic mile of about 1,830m. Putting all these errors together he ended up convinced that the circumference of the world was 25,255kms. Alas, it is 40,000kms, making it an awful lot further to China than Columbus realised.
When the king of Portugal refused to finance his voyage in 1485 it was not because he thought Columbus would fall off the edge of the Earth, but because his experts had warned him that no ship could carry enough supplies to travel those sort of distances. So Columbus pestered Ferdinand and Isabella of Spain for seven years until they finally cobbled together enough money to send him and his ships off on the ocean blue. They never really expected to see him again, and if America had not blocked his route to the lands of silks and spices they wouldn't have.