One day, an old man was out hunting, when he saw a big deer with beautiful horns behind a tree. It was the biggest and finest deer he had ever soon. The hunter was at the top of a cliff, the deer was at the bottom, and there was a wall of rock behind it. The old hunter new that, if he tried to climb down the cliff, the deer would hear and see him; and it was not possible for him to go round the other side of the deer, because the wind was blowing from there, and the deer would smell him at once and run away.
The hunter understood that the only way that he could kill the deer was to shoot at the wall of rock behind the deer. If his bullet hit the rock in the right place, it would jump back from the wall and hit the deer.
So the old hunter began to think. 'Where must I aim my gun so that the bullet will jump back from the wall and kill the deer?' he said to himself. 'There is a strong wind today, so that will turn my bullet a little. How fast is the wind, and how fast does my bullet fly?' He thought carefully about these and other things for several minutes, then he put his gun to his shoulder, aimed it at the exact place on the wall of rock which he had chosen as the correct one, and fired.
The old hunter's plan may have been a very good one, his arithmetic may have been quite correct, and he may have chosen exactly the right place to aim at, but he was not at all good at shooting straight: his bullet did not even hit the wall!