(5) When you start a fire, be to windward of it. Do not attack from
the leeward.
Chang Yü, following Tu Yu, says: 燒之必退退而逆擊之必死戰則不便也 “When
you make a fire, the enemy will retreat away from it; if you
oppose his retreat and attack him then, he will fight desperately,
which will not conduce to your success.” A rather more obvious
explanation is given by Tu Mu: “If the wind is in the east, begin
burning to the east of the enemy, and follow up the attack
yourself from that side. If you start the fire on the east side,
and then attack from the west, you will suffer in the same way as
your enemy.”