An old Zen master always told this fable to unserious students: Late one night a blind man was about to go home after visiting a friend. "Please," he said to his friend, "may I take your lantern with me?"
"Why carry a lantern?" asked his friend. "You won't seen any better with it."
"No," said the blind man, "perhaps not. But others will see me better and not bump into me." So his friend gave the blind man the lantern, which was made of paper on bamboo strips, with a candle inside.
Off went the blind man with the lantern, and before he had gone more than a few yards, Crack! ---someone walked right into him. The blind man was very angry. "Why don't you look out?" he stormed. "Why don't you see this lantern?"
Why don't you light the candle?" asked the other.

from Zen Buddhism: And introduction to Zen with stories, parables, and koan riddles told by the Zen masters. Peter Pauper Press 1959