A scoutmaster was teaching his scouts about survival. "What are the three most important things", he asked, "that you should bring with you in case you get stranded alone in the desert?" Hands were raised to suggest food, matches, distress flares and so on, but one boy said: "A compass, a canteen of water and a deck of playing cards." "Why those items?" asked the scoutmaster. The boy replied: "The compass is to find direction, and the water is to prevent dehydration." "Yes, I understand that," s…