Alas! in naught may one trust the gods against their will!

[Heu nihil invitis fas quemquam fidere divis!]

Virgil (70-19 BC) Roman poet [b. Publius Vergilius Maro; also Vergil]
The Aeneid [Ænē̆is], Book 2, l. 402 (2.402) [Aeneas] (29-19 BC) [tr. Fairclough (1916)]
    (Source)

(Source (Latin)). Alternate translations:

But, ah! what use of valour can be made,
When heav'n's propitious pow'rs refuse their aid!
[tr. Dryden (1697)]

Alas! it is right for one to trust to nothing when the gods are adverse.
[tr. Anthon (1843)]

Alas! on nothing ought man to presume, while the gods are against him!
[tr. Davidson/Buckley (1854)]

Alas! a mortal may not lean
On Heaven, when Heaven averts its mien.
[tr. Conington (1866)]

Alas, one ought
To trust in nothing, when the gods oppose.
[tr. Cranch (1872), ll. 549-550]

Alas that none may trust at all to estranged gods!
[tr. Mackail (1885)]

Alas! what skills it man to trust in Gods compelled to good?
[tr. Morris (1900)]

Ah! vain to boast, if Heaven refuse to aid!
[tr. Taylor (1907)]

But woe is me! If gods their help withhold,
't is impious to be brave.
[tr. Williams (1910)]

Alas! it is not well for anyone to be confident when the gods are adverse.
[Source (1922)]

It is not for men to trust unwilling gods.
[tr. Humphries (1951)]

Ah, well, there's no trusting the gods for anything, once they're against you!
[tr. Day Lewis (1952)]

But oh, it is not right for anyone
to trust reluctant gods!
[tr. Mandelbaum (1971), ll. 540-541]

When gods are contrary
They stand by no one.
[tr. Fitzgerald (1981), ll. 532-533]

But no man can trust in gods who are opposed to him.
[tr. West (1990)]

Never rely on the gods for anything
Against their will.
[tr. Lombardo (2005), ll. 466-467]

But, oh
how wrong to rely on gods dead set against you!
[tr. Fagles (2006), ll. 501-502]

How wrong it is to trust the gods against their will!
[tr. Bartsch (2021)]