be (one's) own worst enemy

To do things that complicate one's life or keep one from success; to be self-destructive or self-sabotaging. Of course Tommy started skipping school again—he's his own worst enemy. She always sabotages a relationship when it's going really well because she's her own worst enemy. Mike gets so anxious on dates that he has a hard time making conversation—he ends up being his own worst enemy.

be your own worst enemy

act contrary to your own interests; be self-destructive.

1993 Richard Lowe & William Shaw Travellers We convinced ourselves that everything was against us but the truth was we were probably our own worst enemies.

be your ˌown worst ˈenemy

be a person who often creates problems or difficulties for himself/herself: He spends all his money on clothes, and then finds that he’s got nothing left to live on — if you ask me, he’s his own worst enemy.

own worst enemy, to be one's

To be the major source of one’s own difficulties. The Greek philosopher Anacharsis (ca. 550 b.c.) already was stating this idea: “What is man’s chief enemy? Each is his own.” Cicero said it of Julius Caesar (Ad Atticum, 49 b.c.). In more recent times, cartoonist Walt Kelly expressed the same thought through his main character, Pogo: “We have met the enemy, and they is us.”