Nothing is so contagious as an example, and our every really good or bad action inspires a similar one.

[Rien n’est si contagieux que l’exemple, et nous ne faisons jamais de grands biens ni de grands maux qui n’en produisent de semblables.]

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

Réflexions ou sentences et maximes morales [Reflections; or Sentences and Moral Maxims], ¶230 (1665-1678) [tr. Tancock (1959)]
    (Source)

In the manuscript and 1665 ed., this concluded "... nor are there any great evils that do not inevitably produce their like [ni de grands maux qui ne produisent infailliblement leurs pareils]."

(Source (French)). Other translations:

There is not any thing so contagious as Example, and whatever actions are done remarkable either for their Goodness or Mischief, they are Patterns to others to do the like.
[tr. Davies (1669), ¶48]

Nothing is of so pestilent spreading a Nature, as Example; and no Man does any exceeding good, or very wicked thing; but it produces others of the same kind.
[tr. Stanhope (1694), ¶231]

Nothing is so contagious as example: never is any considerable good or ill done that does not produce its like.
[pub. Donaldson (1783), ¶122; ed. Lepoittevin-Lacroix (1797), ¶219]

Nothing is so contagious as example. Never was there any considerable good or ill action, that hath not produced its like.
[ed. Carvill (1835), ¶469]

Nothing is so contagious as example; and we never do any great good or great evil which does not produce its like.
[ed. Gowens (1851), ¶241]

Nothing is so infectious as example, and we never do great good or evil without producing the like.
[tr. Bund/Friswell (1871), ¶230]

Nothing is as contagoius as example. Each of our very good or very bad acts reproduces itself.
[tr. Heard (1917), ¶237]

Nothing is so contagious as example, and all our very good or bad deeds beget their like.
[tr. Stevens (1939), ¶230]

Nothing is as contagious as example, and we never perform an outstandingly good or evil action without its producing others of its sort.
[tr. FitzGibbon (1957), ¶230]

Nothing is so contagious as example, and we never commit good or evil acts without their propagating themselves.
[tr. Kronenberger (1959), ¶230]

Nothing is so contagious as example, and we never do either great good nor great evil without producing the like.
[tr. Whichello (2016) ¶230]