A master gardener, famous for his skill in climbing and pruning the highest trees, examined his disciple by letting him climb a very high tree. Many people had come to watch. The master gardener stood quietly, carefully following every move but not interfering with one word. Having pruned the top, the disciple climbed down and was only ten feet from the ground when the master suddenly yelled: “Take care, take care!” When the disciple was safely down an old man asked the master gardener: “You did not let out one word when he was aloft in the most dangerous place. Why did you caution him when he was nearly down? Even if he had slipped then, he could not have greatly hurt himself.” “But isn’t it obvious?” replied the master gardener. “Right up at the top he is conscious of the danger, and of himself takes care. But near the end, when one begins to feel safe, this is when accidents occur.”
Comment: It certainly is the case that accidents tend to occur at the end of the working day when people are comfortable with their surroundings, tired, and let their attention down.
A more technical description is in the short article: Preventing Common Household Accidents
Source: Schloeal, Irmgard; The Wisdom of the Zen Masters, New Directions 1975, Pg 52