If you are a shotgun man you do not need to be told what follows.
At a stationary target, however rapidly you are shooting, you try to hit that object.
In shooting at moving targets you try to make two moving objects (the target and the bullet) meet.
The target is moving. The bullet also takes time to get where the target will be. You have to get the bullet to arrive simultaneously with the target at the same spot.
If you aim at the object, the bullet will arrive at the spot after the object has gone further on.
To give an illustration:
An illustrated paper showed an engraving of a man on a motor bicycle going at fifty miles an hour, at six hundred yards’ distance.
There was a cross made on the man’s chest which, it was explained, was the spot to aim at in order to hit him.
If the rifle were correctly aimed for this cross, a man could shoot millions of shots and never hit the motor-cyclist.
The bullets would reach the spot where the motorist was a moment before, but he would be yards further on when the bullet arrived.