if it's not one thing it's another

if it's not one thing it's another

Если что-то не пошло не так — значит скорее всего это случится с чем-л. другим.

~не одно так другое.

When John lost his keys and his wallet, and his car wouldn't start, he exclaimed in despair, "If it's not one thing it's another."

Ср.: ONE DAMN THING AFTER ANOTHER (ODTAA).