system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Can someone explain how we determine cause of death?

For instance, if someone is obese and is in a car crash and dies, most people say the cause of death is the car crash. But sometimes it's not as clear. For example, suppose someone is obese and gets an illness, and they die. However, they only died because their body was weaker because of their obesity. So if they hadn't been obese they would have survived. Equally, if they hadn't gotten the disease they wouldn't have died. What's the cause of death? Obesity or the disease? Intuitively I want to say the disease, but I feel this has more to do with the fact that diseases (with high mortality) are rare but obesity is not. If everyone was getting this disease, but only obese people died, and obesity was rare, then surely we would say obesity was the cause of death?
gpt
That is exactly why in a death certificate, reasons for death are listed out.

Immediate cause,
Antecedent cause,
Underlying cause,
And other significant condition that could have contributed to death but not related to the disease/condition that caused death.

This will be written like death due to A condition, which is due to B condition, due to underlying C condition, with D condition contributing to it. 

This will paint a vivid picture to anyone wanting to know the reason for death of an individual.