Honestly, some of it is not just will but luck. From a lung perspective, a human with healthy lungs has well over twice the capacity needed to sustain life. If you trash the lungs, but do not cut a major airway or vessel, and don't get a tension pneumo/hemo it is slow'ish (minutes to hours) to kill as pulmonary contusions bloom and other pathologies sap physiologic reserve.
I've seen a black bear shot with a light arrow with a mechanical head that died within 50 feet, the arrow did not pernitrate the mediastinum, however it cut the hilum. The shooter felt the arrow hit too far back, so it was luck in how the shot was pulled, not skill alone that resulted in a quick death. With that arrow, if the shot had been further forward, it would have just taken out the upper lobe of the lung and it is conceivable the bear would have lived.
Mediastinum: The middle compartment in the chest that contains the heart, throat, and other structures.
Hilum: Location where the large bronchi, pulmonary arteries, and pulmonary veins are all clustered together.