I've killed a few big game animals, between a lifetime spent whacking stuff in the USA, Canada and a few trips to Africa. Honestly, I have never had what I would call a bullet failure; not a single one.
Prolly 98% of the critters died, or at least fell, within fifty feet and fully 75+% of them were dead upon impact .. Bang-Flop. Maybe a dozen animals (out of several hundred) staggered to fifty yards. I cannot remember one that went further. And I've never lost a big game animal.
Nope, I've never had a single bullet failure.
BUT, if I'm reading right, a lot of "experts" would think that a more than a few of my bullets experienced what they so knowingly call "failure."
The experts are soooo wise.
Frankly, I'm awfully simple-minded. If a bullet impacts precisely the intended spot and kills the big game animal dead-right-there, I believe that the bullet did not fail. It's as simple as that.
If the bullet will not shoot with acceptable accuracy, or if it is not capable of both penetrating to and destroying the vitals, then the shooter is likely to experience what I would think of as a "bullet failure." I've never been in this situation, mostly because I pick my bullets awfully carefully.
Personally, given today's choices, I believe the shooter is in as much danger of selecting a bullet that is too tough as one that is unacceptably soft.
Just my thoughts......
Steve