dig own grave
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dig (one's) own grave
To do something that has or will have negative consequences that are easily able to be foreseen. If you don't turn in your project, you're digging your own grave. There's no way you'll get a decent grade without it! I'm afraid I'm digging my own grave by turning down the promotion.
dig one's own grave
Fig. to be responsible for one's own downfall or ruin. If you try to cheat the bank, you will be digging your own grave. Those politicians have dug their own grave with their new tax bill. They won't be reelected.