Those who use fire as an aid to the attack show intelligence; those who use water as an aid to the attack gain an accession of strength. By means of water, an enemy may be intercepted, but not robbed of all his belongings.
Sun Tzu spoke of using fire against the enemy, but he was driving at a fundamental tactic: attacking in parallel. One can set fire to an enemy building to drive him out into an ambush. One can set fire to one side of an enemy camp while taking up positions on the other side, again driving the enemy into an ambush. In all cases, the fire is basically used as an extra force of attackers. The fire cannot be reasoned with or bargained with or ignored. The fire has no mercy. While it serves the same function as a band of men would (to attack the enemy and drive him to action), the fire requires no manpower once it is started. It also finds its way inside a barracks without risking the lives of a squad.
Because the fire acts independently, it allows a given group of men to apply more attacking force than would otherwise be possible. Because fire can act as a barrier, it can allow a single group of men to attack from two sides at once without halving their numbers. The lesson is that attacking two times at once is deadly effective.
This is a basic concept in numerous games. In fighting games, projectiles such as “fireballs” are basically independent attacking agents. Once a character spawns a projectile attack, that character is free to move and perform other attacks while the fireball does its thing, allowing basically two attacks at once. The fighting game Marvel vs. Capcom 2 takes this to the extreme, allowing a player to attack not only with projectiles and his main character but also by calling another “assist” character into the battle at virtually any time who performs another attack. This ability to attack in parallel (with the main character and with assist characters at the same time) allows for some incredibly nasty pressure patterns. If the opponent is unable to attack in parallel (if his assist characters are dead) and you are, then your advantage is overwhelming.
Two basic tactics in chess, the fork and the pin, are conceptually similar to attacking in parallel. In a fork, one piece is able to threaten multiple enemy pieces. For example, consider a knight that could move one way to take an enemy bishop or another way to take an enemy rook. If the enemy cannot capture the knight, he will be unable to protect against these two simultaneous threats. He may move the bishop, only to lose the rook, or he may move the rook, only to lose the bishop.
A pin is when a piece threatens an enemy piece, but if that enemy piece is moved out of the way, it merely puts the piece behind it in danger. For example, consider a rook that threatens an enemy bishop several squares away. It is the enemy’s turn to move, but behind his bishop is his king! If the bishop is moved out of the rook’s threat, it merely puts the king in harm’s way. (That’s an illegal move: you can’t move into check.) We say that the bishop is “pinned to the king” in this situation. The rook seems to merely attack one piece, but in a way it’s a double threat. Turn-based games are often about sneaking in what effectively amounts to two moves (two attacks) in one move.
A much more direct example of Sun Tzu’s attacking by fire would be the more literal case of HE-grenades (“high-explosive”) or “flashbang” grenades in the first-person shooter Counter-Strike. Since it takes a couple seconds for a grenade to explode once thrown, the attackers can be fully free to act at the same moment the defenders must deal with the damaging effects of an HE-grenade or the blinding effects of a flashbang. Five players and one well-timed grenade can often have a greater effect than ten players without grenades. “Attacking by fire,” or attacking doubly by using a grenade, projectile, or well-placed chess piece can create an overwhelming advantage.