When we think what we do not feel, we lie to ourselves. We must always think with our whole being, soul and body.

[Penser ce que l’on ne sent pas, c’est mentir à soi-même. Tout ce qu’on pense, il faut le penser avec son être tout entier, âme et corps.]

Joseph Joubert (1754-1824) French moralist, philosopher, essayist, poet

Pensées [Thoughts], ch. 9 “De la Sagesse, de la Vertu, etc. [On Wisdom and Virtue],” ¶ 52, 1798 entry (1850 ed.) [tr. Collins (1928), ch. 8]
    (Source)

(Source (French)). Alternate translations:

To think what we do not feel, is to lie to ourselves. Whatever we think, we should think with our whole being, will and body.
[tr. Calvert (1866), ch. 9]

To think what we do not feel is to lie to one's-self. Whatever we think should be thought by our whole being, soul and body.
[tr. Attwell (1896), ¶ 140]

To think what we do not feel, is to lie to ourselves. Everything that we think we must think with our whole being, soul and body
[tr. Lyttelton (1899), ch. 8, ¶ 38]

To think what we do not feel is to lie to ourselves, in the same way that we lie to others when we say what we do not think. Everything we think must be thought with our entire being, body and soul.
[tr. Auster (1983), 1798 entry]