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A Pyrrhic cost
(lemmy.world)
Explanation: The Greek leader Pyrrhus of Epirus led an army of Greeks in support of Greek city-states in Italy against Rome. While he was an accomplished general, the Roman forces were stubborn, and made Pyrrhus’s victories so costly that he supposedly said “One more such victory against the Romans, and we shall be ruined” giving rise to the phrase “Pyrrhic Victory” for a victory that costs more than it’s worth!