Fortunate people seldom mend their ways, for when good luck crowns their misdeeds with success they think it is because they are right.

[Les gens heureux ne se corrigent guère; ils croient toujours avoir raison quand la fortune soutient leur mauvaise conduite.]

François VI, duc de La Rochefoucauld (1613-1680) French epigrammatist, memoirist, noble

Réflexions ou sentences et maximes morales [Reflections; or Sentences and Moral Maxims], ¶227 (1665-1678) [tr. Tancock (1959)]
    (Source)

First appeared in the 5th Edition (1678).

(Source (French)). Other translations:

Prosperous Persons seldom mend much; they always think themselves in the right, so long as Fortune approves their ill Conduct.
[tr. Stanhope (1694), ¶102]

Fortunate people never correct themselves. They always fancy they are in the right as long as fortune supports their ill conduct.
[ed. Gowens (1851), ¶376]

Lucky people are bad hands at correcting their faults; they always believe that they are right when fortune backs up their vice or folly.
[tr. Bund/Friswell (1871), ¶227]

Happy people rarely correct their faults; they consider themselves vindicated, since fortune endorses their evil ways.
[tr. Heard (1917), ¶373]

Lucky people scarcely ever correct their faults; they always believe that they have acted rightly if fortune has smiled on their evil ways.
[tr. FitzGibbon (1957), ¶227]

Lucky men seldom mend their ways; they always feel in the right so long as luck favors their ill behavior.
[tr. Kronenberger (1959), ¶227]

Prosperous people hardly ever rectify their faults: for while Fortune lends her support to their bad conduct, they always believe themselves to be in the right.
[tr. Whichello (2016) ¶227]