兵势
Combine the orthodox and the surprising — they endlessly generate each other, and victory comes from the surprising. Build momentum like dammed water, and release it at the decisive instant.
What this chapter says
Having covered disposition (form), Sun Tzu turns to 势 — energy, force, momentum. Battle is joined with the orthodox, direct force (正) but decided by the unorthodox, surprising move (奇); and the two are inexhaustible, each giving rise to the other in an endless cycle, like a circle with no beginning or end. The skilled commander builds up potential energy and releases it at exactly the right moment — the rush of pent-up water that rolls boulders, the drawn crossbow loosed in an instant. Crucially, he 'looks to the effect of combined energy, and does not require too much from individuals': victory is sought from the momentum of the whole situation, not squeezed out of heroic individuals. Position ordinary people within an irresistible force and they achieve extraordinary things.
Key lines
Applied today
Pair a solid, expected core with one unexpected move — the surprise is what wins. And time the release of built-up momentum (a launch, a campaign, a market entry) rather than relying on any single person's heroics.
Engineer favorable momentum so ordinary people produce extraordinary results — design the system's force and put good people in it, rather than expecting heroics to compensate for a situation stacked against them.