Two friends got into an argument while walking through the desert, and one friend slapped the other. The friend who was slapped wrote in the sand "Today my best friend slapped me in the face." Later, the same friend saved the other from drowning, and the saved friend wrote on a stone "Today my best friend saved my life." When asked about the different mediums, the saved friend responded that hurts should be written in sand to be erased, but good deeds should be engraved in stone to last forever.