Philippe names the one obstacle Aramis can't scheme around — conscience, remorse — and Aramis answers from the stable: “Le cheval qui a peur du fossé saute au milieu et se tue! L’homme qui croise le fer en tremblant laisse à la lame ennemie des jours par lesquels la mort passe!” Fear doesn't make you careful; it makes you clumsy at the exact wrong moment. The trembling hand opens the guard it meant to protect.

— In our words · Source: The Man in the Iron Mask (Alexandre Dumas)