《六韬·龙韬·军势》
凡是未战而先胜的，都是先示弱于敌，然后进行决战。这样便可事半而功倍。
夫先胜者，先见弱于敌，而后战者也，故事半而功倍焉。
Anyone who wins without fighting first shows weakness to the enemy and then fights the decisive battle. In this way, you can get twice the result with half the effort.