That guy's a beautiful thinker.
My only criticism might be something in line of what panda picked up on but I wouldn't give it that much emphasis because I think this guy did not a great job of qualifying that but well enough and was possibly constrained not to by his topic.
This idea of adversity as some pinnacle of defining the soul. It's a little get off the cross we need the wood but there's also quite a bit of truth to it.
The other conflict with that--particularly as he tried to relate the idea of whatever doesn't kill you makes you stronger with the Buddhist concept of having adversity in life to have opportunities, for instance, to practice compassion--is this awkward sense of the duality of requiring bad for good when the ultimate though often esoteric Buddhist view is the hotdog joke make me one with, that is to say no difference between observer and observed, no duality.
When that's presented as yet un-grappled, but rather so matter-of-factly it can come off as Hemmingway likely would have known though I don't recall that particular line but as Panda brings to mind, a tad mundane, this rationalizing of the horrible things of life.
Here's a fact of life: bad is bad. There's no refuting that. Better to find benefit in bad than bitterness but that doesn't justify the bad because bad is still bad. To think of this transmutation of bad as good is a tool of thinking, not a reality, just as definitions of Nirvana are not Nirvana but may be roads that might lead in that direction.