Knowing what we know today about the shape of the world - which peoples of his time most certainly did not - can you really sit there and say he failed?
Ah, sorry, but this "People thought the world was flat, and Columbus proved that it was round" thing is a myth.
Peoples of the time knew very well the "shape of the world" as roughly spherical. They also knew roughly how large it was -- this had in fact been figured out around 200 BC by Eratosthenes. It was because of this, not a belief in a flat earth, that they thought Columbus was a fool. They knew that the distance to Asia was far too great for it to make sense to take the 'back route' to India. Columbus thought the earth was much smaller than it actually is. He was wrong, they were right.
The thing that was learned was that there was an entire continent there (which had been discovered before but wasn't known to Europeans). But because Columbus was using a grossly wrong value for the earth's size, he didn't even realize what he had discovered and thought he had completed his journey to India on schedule. And so, centuries later, we're still stuck with our "dot or feather" Indians confusion. :P
Anyway, he didn't discover anything about the shape of the earth. And on his mission to find a faster trade route to Asia, he did in fact fail. Of course since the reason for that mission was to make money, you can't really say it was a complete failure from Spain's point of view.