Only cowards kill the vanquished — George RR Martin

You should have learned by now, none of us get the things we want.

He should thank the gods that Ser Rodrik was not ironborn. The men of the green lands were made of softer stuff, though he was not certain they would prove soft enough.

Knights may keep their truces when dealing with other knights, but they are not so careful of their honor when dealing with those whom they deem outlaw.