Nearly everyone takes the limits of his own vision for the limits of the world. A few do not. (Join them.)
Arthur Schopenhauer, Source: The other 90%. How to unlock your vast untapped potential for leadership and life, Crown Business, 2001. quoted on page 154 of The Seven Secrets of Inspired Leaders. How to archive the extraordinary by the leaders who have been there and done it.
Correction: Thanks to SSC, who pointed out that the quote is not the original statement. Here seems to be the more genuine saying:
Every man takes the limits of his own vision for the limits of the world.