una manzana podrida echar a perder el resto de la cesta

= one rotten apple spoils the whole barrel

Ex. His analysis shows that, under certain conditions, there is some truth in the old saying that one rotten apple spoils the whole barrel.

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= one rotten apple spoils the whole barrel

Ex: His analysis shows that, under certain conditions, there is some truth in the old saying that one rotten apple spoils the whole barrel.