Without passion man is a mere latent force and possibility, like the flint which awaits the shock of the iron before it can give forth its spark. – Henri-Frédéric Amiel, Journal, 17 December 1856

The passions are like fire, useful in a thousand ways and dangerous only in one, through their excess. – Christian Nestell Bovee

He only employs his passion who can make no use of his reason. – Marcus Tullius Cicero

Passion, though a bad regulator, is a powerful spring. – Ralph Waldo Emerson