be your own worst enemy

US /bi jʊər oʊn wɜrst ˈɛn.ə.mi/
UK /bi jʊər oʊn wɜrst ˈɛn.ə.mi/
"be your own worst enemy" picture
1.

to cause most of your own problems because of your attitude or behavior

:
He tends to be his own worst enemy, always sabotaging his chances of success.
If you keep procrastinating, you'll be your own worst enemy when the deadline comes.