He turned to leave, but after taking only a couple of steps, he suddenly remembered that when he was a child, he didn't know that these colorful stones were made of glass. He had mistaken them for some mystical stones and begged his mother to buy several of them for him.
Later, when they hurriedly moved to the countryside to live with his grandmother, he'd left those stones behind in a hurry and hadn't played with them since.
This memory made him turn back. He picked up the lonely stone and tucked it into his jacket pocket.