Water

One of the most successful strategy in Age of Empires II: The Conquerors (AOC) is the use of Knight Rush. It means that players will try their best to go to the Castle Age as soon as possible (around 16 minutes) in order to start the raiding by some Knights, which can only be produced during the Caste Age.

Like most strategy textbooks says, time means everything in war (兵貴神速). Provided that Knights have high mobility and attacking power, they are the best options to start a quick war to destroy the economics of the enemies. It is an appealing tactics that the opponents can hardly defend in that early stage. Even they decide to defend by developing anti-knight units, the cavalry can still be managed as defensive units. When the enemies comes, Knight units are still the most reliable units, with their speed and armors.

You see, the Knight units in the game is just like water. It can be still but can be aggressive. Water can flow and water can crash, as mentioned by Bruce Lee.

天下莫柔弱於水，而攻堅強者莫之能勝，其無以易之。「弱之勝強，柔之勝剛」，天下莫不知，莫能行。是以聖人云﹕「受國之垢，是謂社稷主；受國不祥，是爲天下王。」正言若反。  (道德經)