Nothing in the world can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated failures. Persistence and determination alone are omnipotent.
— Calvin Coolidge, 1872.
Someone posted this one somewhere. It's interesting because I've met loads of people who believe they're particularly intelligent and it is just their lack of hard work that's prevented them from being big. Each, however, believes that they're one of very few like that.