Sun Tzu actually devotes an entire chapter to fire. It's that important!
From XII. THE ATTACK BY FIRE:
1. Sun Tzu said: There are five ways of attacking
with fire. The first is to burn soldiers in their camp;
the second is to burn stores; the third is to burn
baggage trains; the fourth is to burn arsenals and magazines;
the fifth is to hurl dropping fire amongst the enemy.
5. In attacking with fire, one should be prepared
to meet five possible developments:
6. (1) When fire breaks out inside to enemy's camp,
respond at once with an attack from without.
7. (2) If there is an outbreak of fire, but the enemy's
soldiers remain quiet, bide your time and do not attack.
8. (3) When the force of the flames has reached its height,
follow it up with an attack, if that is practicable;
if not, stay where you are.
9. (4) If it is possible to make an assault with fire
from without, do not wait for it to break out within,
but deliver your attack at a favorable moment.
10. (5) When you start a fire, be to windward of it.
Do not attack from the leeward.
This chapter on fire veers off in another direction though:
17. Move not unless you see an advantage; use not
your troops unless there is something to be gained;
fight not unless the position is critical.
18. No ruler should put troops into the field merely
to gratify his own spleen; no general should fight
a battle simply out of pique.
19. If it is to your advantage, make a forward move;
if not, stay where you are.
Oh, and a great example of magic contradicting sound real-world advice:
21. But a kingdom that has once been destroyed can
never come again into being; nor can the dead ever
be brought back to life.
Thus spake Sun Tzu.