Literature Reference: 投沙拥海水，安得久不翻。 —— 《长城》 Throwing sand into the sea, how can it not be overturned? Source from 'The Great Wall'.
投: Tendency. To cast, to hurl, to throw. Use with caution.
沙: Sand, grains of sand.
Meaning: Throwing sand into the sea symbolizes perseverance despite the insignificance of one's efforts.