shaman,
If we hunt long enough we will run into animals that really don't want to die, despite being hit precisely in the vitals, even with Wonder Bullets. I've probably seen it with pronghorns more than deer, but deer will definitely resist going gently into that good night.
Once shot a big mule deer buck at about 275 yards with a 160-grain bullet from a 7x57, muzzle velocity about 2700 fps. This would seem to be sufficient, and at first it looked like it was. The buck was quartering, and I put it in the left shoulder to go back through the chest cavity. The buck staggered around a few seconds and then fell.
Low brush covered the ground and he fell behind some. As I walked up, expecting find him laid out peacefully, his head was up, and as I approached he stood and started running away. I put another bullet between his cheeks, which dropped him.
The first bullet had gone right where it was supposed to, traversing the chest and doing much damage, ending up under the hide under the short ribs on the other side, perfectly mushroomed.
But he did not want to die--and that was just one example. Also saw a big buck pronghorn take several 120-grain .25 caliber bullets in the chest before he gave up, and after the first one a wide spout of blood was pulsing out of his chest, through the exit wound just behind his shoulder. In neither instance was the fault the cartridge's or the bullet's or the shooter's.
Have also seen the opposite a few times, when much bigger animals dropped more-or-less instantly to bullets through the chest cavity, bullets that would be regarded as inadequate by many members of the Campfire. Dunno what causes that either, but am far more puzzled when they keep living when their lungs and heart are essentially gone.
