Give him enough rope and he'll hang himself

Cultural  

1. A person will bring about his or her own misfortune if given the opportunity.

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Example Sentences

I think this one has been used so much in so many different eras that we can lodge it in the same category of “if you lie down with dogs, you wake up with fleas” and “give him enough rope and he’ll hang himself.”

From Fox News

"Well, 'give him enough rope and he'll hang himself,' as they say," rejoined Mr. Munster—"that is, if your ideas about him are true."

From Project Gutenberg