There are seven grains of sand in the world. One grain fell into a shell, and after a long time, it finally turned into a pearl; one grain fell on the seaside, and became a beach that rose and fell with the sea; one grain was blown by the wind, and became mist in the air; one grain fell in the desert, and was exposed to the sun for life; one grain was mixed into the mud and rocks, and was built into roads or bridges by people; one grain fell in the eyes of the girl, and followed the girl's tears; and one grain was in your heart, and occasionally felt heartache to feel its existence. No matter who you are or who you love, you have seen them and they have made you laugh, cry and despair.