Snatch-the-pebble Definition

verb

(colloquial, idiomatic) To fully grasp the meaning of a concept or developed a skill to a high degree of proficiency, often that rivals some specific expert.

Wiktionary

Origin of Snatch-the-pebble

From the 1970s television series called Kung Fu starring David Carradine. In the title sequence to this series, the protagonist (a young martial arts student) is finally able to snatch a pebble from his master's hand, indicating he has developed sufficient skills and wisdom and is ready to leave the school and venture into the world.

From Wiktionary