system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some people survive massive trauma/blood loss, while others don't?

I've watched a lot of shark attack videos (we all need something, right?) and I just don't understand why some people will lose entire limbs (and therefore butt tonnes of blood) and will survive, while others will only lose a large amount of flesh/tissue from a limb, and will survive.

To give two examples:

1. Woman is swimming, shark bites off entire leg (I think halfway through the femur). She is on a ship in the middle of the ocean. She survives. 

2. A woman is swimming on a beach and struggling, so life guards come to rescue her. A shark attacks her, biting off her calf. She is rescued by lifeguards within seconds. She is taken back onto the beach, where the lifeguards don't apply pressure bandages/tourniquets (therefore I'm assuming she;s already dead?) Either way woman dies.
gpt
1. The human body is ridiculously inconsistent. One person can die from a fall of a meter, one survived a fall of several kilometers.

2. Previous medical issues. If girl on beach is on blood thinners, she might bleed out.

3. To use your example, when you have an entire limb severed, the muscles contract and form a makeshift torniquet for the wound, which would have probably happened for the first one, not the second.

4. Your examples are both marked '1.'