shoot oneself in the foot

Idioms  

1. Foolishly harm one's own cause, as in He really shot himself in the foot, telling the interviewer all about the others who were applying for the job he wanted. This colloquial term alludes to an accidental shooting as opposed to a deliberate one done so as to avoid military service.

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Example Sentences

"When we graduate from traditional statistical methods to machine learning methods, there are a vastly greater number of ways to shoot oneself in the foot," said Narayanan, director of Princeton's Center for Information Technology Policy and a professor of computer science.

From Science Daily

But to treat quitting as inevitable is to shoot oneself in the foot.

From Seattle Times