A number of people believe the Washington Irving myth that Columbus was the first to figure out the Earth was round and that sailing west would not lead to certain doom. This is however clearly false. There was a disagreement between Columbus and the intellectuals of the time, mainly the distance to Asia going east and the circumference of the Earth. He figured it was about three thousand miles traveling west to hit India, everybody else said it was probably about 11,000 miles, and he would die sailing through the great "Ocean Sea" which covered 180 degrees of the world.
Now, it turns out that the great minds of the time were right on both counts, the distance to India going east as well as the circumference of the Earth to a remarkable degree. He was pretty clearly rebuked by everybody because he was pretty clearly wrong on both these counts. Though, the wrong assumption that the span between Europe and Asia was only water was made on both sides.
Why then did the new Spanish Monarchs fund his journey? Why spend a lot of money funding a fool's errand? Drugs. When the Muslims took over Spain and were later cast out they left a rather interesting legacy: Opium addiction. They were desperate to find a better way to India because they needed a fix. After Ferdinand and Isabella managed to drive the last of them out, they were left with a rather bad drug problem and no supplier. They gave him unusually generous terms, partially because it was doubtful he was going to return, and an order for opium.
Christopher Columbus was wrong on every count, had stupid ideas, and was rightfully rebuked. Finally, though finances were short he was sent on a drug run to India. He was so foolish he believed he actually made it (hence the word "Indians" for Native Americans) and refused to hear otherwise and died believing he was right.