Two friends were walking through the desert. In a specific point of the journey, they had an argument, and one friend slapped the other one in the face. The one, who got slapped, was hurt, but without anything to say, he wrote in the sand: "TODAY, MY BEST FRIEND SLAPPED ME IN THE FACE". 

They kept on walking, until they found an oasis, where they decided to take a bath. The one who got slapped and hurt started drowning, and the other friend saved him. When he recovered from the fright, he wrote on a stone: "TODAY MY BEST FRIEND SAVED MY LIFE". 

The friend who saved and slapped his best friend, asked him, "Why, after I hurt you, you wrote in the sand, and now you write on a stone?"

The other friend, smiling, replied: "When a friend hurts us, we should write it down in the sand, where the winds of forgiveness get in charge of erasing it away, and when something great happens, we should engrave it in the stone of the memory of the heart, where no wind can erase it" 

Learn to write in the sand.