Rage.
That's not a word or emotion a warrior poet takes lightly. It's an emotion that if channeled properly can be used effectively, but if allowed to go unchecked leads to one's own destruction. Rage most assuredly didn't overcome the Vikings in Philadelphia did so much as incompetence did...but in the aftermath of the Letdown at the Linc rage is what consumed Mike Zimmer.
[ED NOTE: Also, if you're a fan of The Walking Dead, don't read the first paragraphs that has asterisks, or the asterisks, because I give away a spolier. And rage is what you will feel if you haven't seen it yet.