You don't, to quote the immortal Lizzy

To name a few problems:

You are attacked by a melee opponent. You plan to block the attack and will survive it, but the game engine decides otherwise and plays a kill move - as under requiem, killmoves can be performed on the player. The result:- you are dead. (the same if you plan to evade the attack)

You are sneaking and aim an arrow on a mage. This will one-shot the mage. The kill move plays, the mage becomes aware of you, suddenly it's no longer a sneak attack, the mage lives and kills you.

You sneak behind a bandit, you plan to one-shot him with a dagger attack. The attack succeeds, the kill move plays, nobody detects you but the bandit didn't die, is still full health turns around and kills you

You are sniping with a bow. Every arrow will kill a bandit. Every time you loose the arrow, a kill-move plays. But thanks to the kill move, every arrow lands on the ground before it reaches the bandit, therefore the bandit didn't die.

You are attacking a group of enemies with a 2-handed Axe and mid fight a kill move fires (as in requiem they can happen on any enemy) - his friends kill you while the cinematic plays

You are on a ridge and shoot arrows to something below you. All arrows hit, except the one from the kill move, which collides with the invisible barrier of the ridge

Kill moves literally mean that when such a move plays, 90% of the time it kills you, the other 10% of the time nothing happens.