有这么一个故事:有一个参加长跑比赛的选手在经过一片沙滩时,鞋子里灌满了沙子。他匆匆把鞋子脱下,胡乱地把沙子倒出,便又急忙继续往前跑。可是有一粒沙子仍留在他的鞋里。在以后的路程中,那粒沙子磨着他的脚,使他走一步, There is such a story: There is a player who participates in a long-distance running game. When passing through a beach, the shoes are filled with sand. He hurriedly took off his shoes, poured the sand out of his hands, and quickly ran forward again. But a grain of sand remained in his shoes. In the following journey, the grain of sand rubbed his feet and made him take a step.