the strong do what they can and the weak suffer what they must

Calque of Ancient Greek δυνατὰ δὲ οἱ προύχοντες πράσσουσι καὶ οἱ ἀσθενεῖς ξυγχωροῦσιν (dunatà dè hoi proúkhontes prássousi kaì hoi astheneîs xunkhōroûsin) in Thucydides’s History of the Peloponnesian War 5.89 (the Melian dialogue). Thucydides presents the sentence as part of an ultimatum from Athens to the city of Melos demanding tribute. The Melians having rejected the order, their city was taken by force and their population enslaved and massacred by the Athenians. The following year, Athens suffered a serious defeat that lead to its conquest by Sparta. The wording that has become standard is from Richard Crawley’s 1874 translation.

来源：wiktionary