Complicated stuff. Though I do reject the idea that Benoit was this normal guy who happened to succumb to brain damage. Not saying that the concussion damage didn't play a big role, but honestly...bits and pieces that have come out about his personality, especially from Jericho, make him seem like he was a bit of a weird dude from day one.
And the roid rage thing.... I was always so against that idea, but I think it factored in, depending on what he was taking. Read any steroid forum and check out posts from people who've taken Tren. Definitely some mental side effects for a lot of people, including anger issues. It's well known.
And his personal life was a living hell. Having that many close friends die in succession is brutal. I'm sometimes shocked Bret hasn't struggled with suicide, given how many friends/family members he's lost. That takes a massive toll on anyone.
So, weird guy + brain damage + sad life circumstances + (maybe) steroids/alcohol abuse = what we got
a perfect storm of shyt, really.