【明報專訊】To those who explore for precious minerals such as gold, silver, oil, etc, pay dirt is any valuable underground mineral. Some people are constantly searching for those things, and when they find them they are said to strike pay dirt. From that, we strike pay dirt whenever we obtain something useful or valuable. "Grandma worked hard growing roses, but she said it was worth it when she struck pay dirt and won first prize for them at the fair!"