If you attack a mathematical problem directly, very often you come to a dead end, nothing you do seems to work and you feel that if only you could peer round the corner there might be an easy solution. There is nothing like having somebody else beside you, because he can usually peer round the corner.

Collected Works: Michael Atiyah Collected Works: Volume 1: Early Papers; General Papers (ed. Oxford University Press, 1988) - ISBN: 9780198532750