We did not manage to find the exact quote, but we suppose (though not sure) that Stefan Sagmeister told the next thing: «Extraordinary amazing work is the same as good one, but pushed as hard as possible».

This amazing feeling when you reach the perfect idea is the best moment in life for any creative person, but after you have this idea in your mind that is when you get your chance to create something really remarkable. But for this, you have to push a lot. And push really really hard (of course you have to be careful and split perfectionism and high standards — avoid the first or you get mad fast).