Of course, every thoughtful person realizes that few effects in life are due to one cause only, and that most effects are due to a combination of many causes; so that, if any weapon or method succeeds or fails, it is illogical to infer from that one fact that the weapon or method is good or bad.

A common illustration is the well-known fact that a marksman may hit the target when his aim is too high or too low, provided that he has erroneously set his sight enough too low or too high to compensate; whereas if he had made only one error instead of two, he would have missed.

"Two wrongs cannot make a right," but two errors can compensate each other, and often do.

The theory of the Probability of Errors recognizes this.

In fact, if it were not true that some errors are plus and some minus, all errors in gunnery (in fact in everything) would be additive to each other, and we should live in a world of error.
The partial advantage of the game-board over the occurrences of actual war, for the purpose of studying strategy, lies largely in its ability to permit a number of trials very quickly; the trials starting either with identical situations, or with certain changes in conditions.