A General, after gaining a great victory, was encamping with his army for the night. He ordered sentinels to be stationed all round the camp as usual. One of the sentinels, as he went to his station, grumbled to himself, and said, "Why could not the General let us have a quiet night's rest for once, after beating the enemy? I'm sure there's nothing to be afraid of."
The man then went to his station, and stood for some time looking about him. It was a bright summer's night, with a harvest moon, but he could see nothing anywhere: so he said, "I am terribly tired. I shall sleep for just five minutes, out of the moonlight, under the shadow of this tree." So he lay down.
Presently he started up, dreaming that some one had pushed a lantern before his eyes, and he found that the moon was shining brightly down on him through a hole in the branches of the tree above him. The next minute an arrow whizzed past his ear, and the whole field before him seemed alive with soldiers in darkgreen coats, who sprang up from the ground where they had been silently creeping onward, and rushed towards him.
Fortunately the arrow had missed him; so he shouted aloud to give the alarm, and ran back to some other sentinels. The army was thus saved; and the soldier said, "I shall never forget, as long as I live, that when one is at war one must watch."
Edwin Abbott Abbott, Parables for Children.