When the enemy is too strong to attack directly, then attack something he holds dear. Know that in all things he cannot be superior.

Somewhere there is a gap in the armour, a weakness that can be attacked instead.

Related story:

This strategy derives its name from a famous incident that occurred in 354 BC. At this time one of China's most renowned strategists, Sun Bin (A descendent of the even then famous Sun Zi) was an advisor to the king of Qi. Sun had earlier been at the court of Wei but another minister, Pang Juan, became jealous of Sun's cleverness. Through court intrigues he had Sun framed as a spy, sentenced to mutilation, and imprisoned. Sun escaped and fled to Qi. Several years later the king of Wei appointed the same Pang Juan as commander of the army and sent him to attack the capital of Zhao. The king of Zhao immediately appealed to Qi for help. The king of Qi consulted his advisors who all spoke in favour of rushing to aid their ally, only Sun Bin recommended against attacking. Sun advised: " To intervene between two warring armies is like trying to divert a tidal way by standing in its path. It would be better to wait until both armies have worn themselves out." The king agreed to wait.

The siege of Zhao had lasted more than a year when Sun Bin decided the time was ripe to come to Zhao's aid. The king of Qi appointed prince Tian Ji as general and Sun as military advisor. Tian Ji wanted to attack the Wei forces directly to lift the siege of Zhao, but again Sun advised against direct intervention saying: " Since most of Wei's troops are out of the country engaged in the siege, their own defence must be weak. By attacking the capital of Wei, we will force the Wei army to return to defend their own capital thereby lifting the siege of Zhao while destroying the Wei forces in turn." Tian Ji agreed to the plan and divided his army into two parts, one to attack the capital of Wei, and the other to prepare an ambush along the route to the capital.

When the Wei general Pang Juan heard that the capital was being attacked, he rushed his army back to defend the capital. Weakened and exhausted from the year long siege and the forced march, the Wei troops were completely caught by surprise in the ambush and suffered heavy losses. Chao was thus rescued while Pang Juan barely escaped back to Wei to recoup his losses. Sun Pin would later defeat his nemesis Pang Juan using another classic strategy.