Lucky yet sad? My friend, should Fortune find
You lacking gratitude, she’ll change her mind.

[Tristis es et felix. Sciat hoc Fortuna caveto:
Ingratum dicet te, Lupe, si scierit.]

Martial (AD c.39-c.103) Spanish Roman poet, satirist, epigrammatist [Marcus Valerius Martialis]

Epigrams [Epigrammata], Book 6, epigram 79 (6.79) (AD 91) [tr. B. Hill (1972)]
    (Source)

"To Lupus." (Source (Latin)). Alternate translations:

Th' art rich & sad; take heed lest fortune know;
She 'll call th' unthankefull, Lupus, if she do.
[tr. May (1629)]

How? sad and rich? Beware lest Fortune catch
Thee, Lupus, then she'll call thee thankless wretch.
[tr. Fletcher (1656)]

Th'art rich and sad; take heed lest Fortune see,
And, as ungrateful, do proceed with thee.
[tr. Killigrew (1695)]

What! sad and successfull! let Fortune not know.
Ingrate! would she brand thee, did she see thee so.
[tr. Elphinston (1782), Book 12, ep. 88]

You are sad in the midst of every blessing. Take care that Fortune does not observe, or she will call you ungrateful.
[tr. Bohn's Classical (1859)]

You are sad, although fortunate. Take care Fortune does not know this; "Ingrate" will be her name for you, Lupus, if she knows.
[tr. Ker (1919)]

In spite of your luck you seem gloomy of late:
Take care, or Dame Fortune will dub you 'Ingrate.'
[tr. Pott & Wright (1921)]

You are sad and lucky. Mind you don't let Fortune know. She will call you ungrateful, Lupus, if she gets to know.
[tr. Shackleton Bailey (1993)]

Lupus, you're sad, though lucky. Don't disclose it.
Fortune will call you thankless if she knows it.
[tr. McLean (2014)]

You've got it all, Lupus, but you're glum, moping, dour.
Do you want Fortune to think you're ungrateful to her?
[tr. D. Hill (2023)]