I speculate, but there might also be a part where simply more people suffered from heat strokes in the past when extreme temperatures occurred. So part of the answer of "how did people live before ACs were invented?" is that some didn't.
My observation is that Vietnamese people know about the risk of heat stroke and how to avoid it.
You won’t see people walking around outside during the hottest hours (9am to 5pm). People are in the shade, avoid physical activity.
There are some manual laborers working outside at those hours, but they are covered from head to toe to protect against the sun and take frequent breaks in the shade.
But heat tolerance is real. Many people live without AC, and even those with it often won’t use it except for the hottest few days of the year.
It will be 35C with 50% humidity (41C heat index) and they aren’t sweating.
I don't doubt that general heat tolerance isn't real for the healthy part of the population. However the hottest days could hit elderly and unhealthy people especially hard (or even the healthy, if it's especially hot).
> Many people live without AC, and even those with it often won’t use it except for the hottest few days of the year.
