One day, a boy comes across a string of beads. One bead is made of clay. The second bead is filled with water. The third bead is filled with air, and the fourth bead is made of wood.

 

The boy is overjoyed. He ties one end of the string around his belt and goes back to playing. The bead on the other end of the string drags below his feet, but the boy doesn’t pay heed.

 

When the boy reaches home, he unties the string to show to his mother. To his dismay he finds that with the last bead gone, all the others have slipped off as well.