Required cards

A novice mountaineer is about to conquer the summit of a mountain. An elderly guide asks: “Did you take a pack of playing cards with you?” “Why?” “When I was young and unfamiliar with the mountains, I always took a pack of cards with me. When I got lost, I sat down and started playing solitaire.” “And did that help?” “Of course! Sooner or later, some idiot would appear behind me and start giving me advice on where to put a card.”