It is the head that governs men. A kind heart is of no use in a chess game.

[On gouverne les hommes avec la tête. On ne joue pas aux échecs avec un bon cœur.]

Nicolas Chamfort (1741-1794) French writer, epigrammist (b. Nicolas-Sébastien Roch)

Products of Perfected Civilization [Produits de la Civilisation Perfectionée], Part 1 “Maxims and Thoughts [Maximes et Pensées],” ch. 8, ¶ 522 (1795) [tr. Merwin (1969)]
    (Source)

(Source (French)). Alternate translations:

People are governed with the head; kindness of heart is little use in chess.
[tr. Mathers (1926)]

Men are governed using the head. A kind heart is useless in a chess game.
[tr. Dusinberre (1992)]

A person governs men with his head. One does not play chess with goodness of heart.
[tr. Siniscalchi (1994), ¶ 521]