4 ideas
The final stratagem holds that when every other option has failed, running away is the best choice, because retreat keeps your forces intact while defeat or surrender destroys them. Fleeing is treated as a rational move that keeps future options open, not as a moral failure.
The thirty-six stratagems are grouped into six sets of six, organized by situation: when winning, when facing an enemy, when attacking, in confused situations, when gaining ground, and when losing. The right move depends on diagnosing your relative position first, then choosing from the set that fits it.
Instead of meeting a strong enemy head-on where it is concentrated, attack something it values that it has left weakly defended, forcing it to pull back. Named after a Warring States campaign in which Qi relieved the siege of Zhao's capital by marching on the undefended capital of Wei, whose army then had to withdraw.
Stratagems such as 'deceive the heavens to cross the sea' rely on the fact that attention fades for things seen often. By making a real move look routine or openly visible, you get it past an observer who is only watching for hidden, unusual actions.