User blog comment:WarrenWitch/Aura/@comment-17099359-20141027100217/@comment-25436196-20141027172817

I imagine there is probably a limit to the amount of protection provided by a person's Aura. For example, it can prevent your skull from being cracked open when hit against the ground, but it doesn't prevent you from losing consciousness because of the hit. Just look at Ren, back in Volume 1: he passed out after being thrown against the ruins, but he didn't have a single fracture on him. Maybe it can fully negate damage when it's 100% active, but in its dormant state, it just makes sure you won't die from certain hits. And who knows, maybe unleashing the Aura's full capacity needs a lot of concentration, and most people aren't skilled enough to just do it in the heat of the moment

Also, if a person's Aura gets drained the more damage they receive, then getting a major blow, like being hit by a truck, or shot in the face with what I imagine were Remnant's equivalent to armor-piercing rounds, could just deplete it all at once and kill the person. Or it could be that Tukson just wasn't very proficient with his Aura control: we know that it needs to be "unlocked" in one way or another, and that controling it properly requires some training, so maybe Tukson just focused on being as strong as he could be, and never thought about learning how to control the one thing that could same him from a headshot