Moral Letters to Lucilius Section 21

Si est aliquis minus beatus quam alius, sequitur, ut hic alterius vitam beatioris magis concupiscet quam suam. Beatus autem nihil suae praefert. Utrumlibet ex his incredibile est: aut aliquid beato restare, quod esse quam quod est malit, aut id illum non malle, quod illo melius est. Utique enim quo prudentior est, hoc magis se ad id, quod est optimum, extendet et id omni modo consequi cupiet. Quomodo autem beatus est, qui cupere etiamnunc potest, immo qui debet?

Qu’un homme soit moins heureux qu’un autre, naturellement il ambitionnera cette vie
plus heureuse que la sienne. Or l’homme vraiment heureux ne préfère rien à son sort. Il est de même peu croyable qu’il reste quelque chose que le sage aime mieux être que ce qu’il est, ou qu’il ne préfère pas ce qui serait meilleur à ce qu’il a. Car assurément, plus il sera sage, plus il se portera vivement vers la meilleure des situations et voudra la conquérir à tout prix. Or comment serait heureux l’homme qui peut encore, que dis-je ? qui doit encore désirer quelque chose ?

If one person is less happy than another, it follows that he eagerly desires the life of that other and happier man in preference to his own. But the happy man prefers no other man’s life to his own. Either of these two things is incredible: that there should be anything left for a happy man to wish for in preference to what is, or that he should not prefer the thing which is better than what he already has. For certainly, the more prudent he is, the more he will strive after the best, and he will desire to attain it by every possible means. But how can one be happy who is still able, or rather who is still bound, to crave something else?