Two brothers returned from a hunt to find that their tribe had packed up and left them stranded in the desert.
The elder, stronger brother gathered six days of water into skins, and gave three days' worth to his younger, weaker brother.

They traveled for four days, never catching up to their tribe.
Each day, the younger brother drank his fill of water while the older, stronger brother drank only half a ration, looking with disapproval at his brother's gluttony.
On the morning of the fourth day, as the younger brother drained the last drops from his water skin, the elder brother finally spoke:
"It may be days more until we catch up to the tribe, brother. I have saved my water, though it cost me discipline and sacrifice. You have drunk your water and have no more. Now your gluttony will be your downfall."

"Not so, brother," replied the younger, drawing his dagger. "My water packs have been lighter the past three days, and my body is refreshed from its fill of water. You are tired from carrying your load, and weak from deprivation. Now I am the stronger..."