We are never quite as happy, or as unhappy, as we think.

[On n’est jamais si heureux ni si malheureux qu’on s’imagine.]

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

Réflexions ou sentences et maximes morales [Reflections; or Sentences and Moral Maxims], ¶49 (1665-1678) [tr. FitzGibbon (1957)]
    (Source)

Present in the first edition. In the first four editions, the concluding words were "... que l’on pense [whatever one thinks]." In the manuscript, this maxim read:

One is never so unhappy as one fears, nor so happy as one hopes.
[On n’est jamais si malheureux qu’on craint, ni si heureux qu’on espère.] 

Another manuscript version is what the Davies translation below derives from:

Les biens et les maux sont plus grands dans notre imagination qu’ils ne le sont en effet, et on n’est jamais si heureux ni si malheureux que l’on pense.

Above notes. (Source (French)). Alternate translations:

Goods and Evils are much greater in our imaginations of them, than they are in effect; and men are never so happy or unhappy, as they think themselves.
[tr. Davies (1669), ¶128; see above.]

None are either so happy or so unhappy, as they imagine.
[pub. Donaldson (1783), ¶211; ed. Lepoittevin-Lacroix (1797), ¶49]

No person is either so happy;, or so unhappy, as he imagines.
[ed. Carville (1835), ¶184]

We are never so happy, or so unhappy, as we imagine.
[ed. Gowens (1851), ¶50]

We are never so happy or so unhappy as we suppose.
[tr. Bund/Friswell (1871); tr. Stevens (1939)]

We are never as happy or unhappy as we think.
[tr. Heard (1917)]

We are never so happy or so unhappy as we think.
[tr. Kronenberger (1959)]

We are never as fortunate or as unfortunate as we suppose.
[tr. Tancock (1959)]

We are never so happy nor so unhappy as we imagine.
[tr. Whichello (2016)]