be one's own worst enemy

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be one's own worst enemy (third-person singular simple present is one's own worst enemy, present participle being one's own worst enemy, simple past was one's own worst enemy, past participle been one's own worst enemy)

1. (idiomatic) To cause problems for one's self, act contrary to one's own interest, self-sabotage.
   • 1870, Mary Dwinell Chellis, Mark Dunning's Enemy‎, page 27:

     “Mark is his own worst enemy. Good night.” True. No enemy however powerful and malicious, can so work a man's ruin as his own unbridled passions and depraved appetites.

   • 1881 [1589], Charles Thornton Forster & F.H. Blackburne Daniell, The Life and Letters of Ogier Ghiselin de Busbecq‎, translation from the Latin of Legationis Turcicae epistolae quatuor by Ogier Ghiselin de Busbecq, page 221:

     For each man is his own worst enemy, and has no foe more deadly than his own intemperance, which is sure to kill him, if the enemy be not quick.

• “be one's own worst enemy”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.
• “be your own worst enemy” in Longman Dictionary of Contemporary English, Longman.
• “be your own worst enemy” in the Cambridge English Dictionary, Cambridge: Cambridge University Press.
• “be your own worst enemy” (US) / “be your own worst enemy” (UK) in Macmillan English Dictionary.