So his payoff, the attacker's payoff,

入侵者的收益
is how many battalions does he get to bring into your country?

是他攻入你国家时还剩余多少兵力
He only has two to start with and for you,

他只有两个营的兵力
it's how many battalions of his get destroyed?

而你的收益是入侵者损失多少兵力
So just to give an example,

举个例子吧
if he goes through the hard pass and you defend the hard pass,

如果入侵者与你在崎岖之途上狭路相逢
he loses one of those battalions going over the mountains

他在翻越山岭时损失一营
and the other one because he meets you.

与你交战再损失一营
So he has none left and you've managed to destroy two of them.

那么他全军覆没而你得到一场完胜
Conversely, if he goes on the hard pass

相反如果他选择崎岖之途
and you defend the easy pass,

而你却防守平坦之路
he's going to lose one of those battalions.

那么他仅仅损失一个营的兵力