Bob is a normal adventurer, traveling with a small caravan from point A to point B. Sudden;y, the group is attacked by a monster Bob has never seen before! The group rallies and drives the beast off, but not before the beast sting/scratches/bites/etc Bob, and he has fallen deathly ill/unconscious/stark raving mad. The wise cleric attempts healing, but warns that it's pretty much hit or miss. There is a good chance Bob will die.... but if he does, he will be stronger, faster, have night vision, be immune to the poison that did this in the first place, and have refreshingly fresh breath forever.
Of course, our hero is made of that sterner stuff.
Basically, something has happened to a character that USUALLY means they should be sized for a pine box. Once in a while though, someone pulls through with new and fantastic abilities. I do not mean a story where a character regularly doses themselves with something highly lethal until they become immune, I mean when someone has a near-lethal brush with the rare and exotic, and instead of dying in agony, they eventually walk it off, and are better off for it.
I also don't mean when a character undergoes some sort of insanely dangerous training and comes back having taken a level in bad ass. I'm talking more of a.. this thing happened, and now I guess I'm awesome.
I'm also trying to think of examples not from comic books, but since I had the thought all I've been able to come up with is how many of our favourite capes and cowls should have outright died in their origin stories..