"Hit pay dirt" is a colloquialism meaning to strike it lucky or find success. It's an expression that's often used to describe someone who's achieved an unexpected and significant breakthrough. Synonyms for "hit pay dirt" include striking gold, striking a vein, hitting the jackpot, hitting the bullseye, hitting the mark, scoring big, and finding the mother lode. Other expressions with a similar meaning include hitting the sweet spot, the big time, or the big league. Whatever the terminology, these expressions describe that feeling of great satisfaction and accomplishment that comes with achieving something significant after persistent effort and dedication.