Ambition and perseverence is really the key. Over and over again, I've read of famous people attributing their success to perseverence.

Some examples:

"Godlike genius.. Godlike nothing! Sticking to it is the genius! I've failed my way to success." -- Thomas Edison

"Let me tell you the secret that has led me to my goal. My strength lives solely in my tenacity." -- Louis Pasteur

"Men give me credit for genius; but all the genius I have lies in this: When I have a subject on hand I study it profoundly." -- Alexander Hamilton

"What I had that others didn't was a capacity for sticking to it." -- Doris Lessing