Ambitious Men cheat themselves, when they fix upon any Ends for their Ambition; those Ends, when they are attained to, are converted into Means, subordinate to something farther.

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

Réflexions ou sentences et maximes morales [Reflections; or Sentences and Moral Maxims] (1665-1678) [tr. Stanhope (1694), Part 4, ¶65]
    (Source)

Reported in multiple translations, but no modern ones. I cannot find the analog for it, the French original, or the "official" number.

Appears in the 1706 (Powell) ed. of Stanhope as ¶711.

Other translations:

The ambitious deceive themselves in proposing an end to their ambition; for that end, when attained, becomes a means.
[pub. Donaldson (1783), ¶32]

When the ambitious propose an end to their ambition, they deceive themselves; for, when attained, the end becomes a mean.
[ed. Carville (1835), ¶29]