I live in a pretty hot climate, but it’s only really unbearable at times due to shoddy building and bad urban planning. Even then, summer can be difficult.
I can’t imagine what it’s like on the equator, especially in dense urban centres. What’s Mumbai, Bangkok, or Singapore like at the height of the wet season?! How do millions of people function day to day?
Slightly different from your question, but in Egypt we get through it by not having a wet season. The Egyptian summer is very dry and rain only falls in the winter, so we just… Exist I guess. People who grew up in a certain temperature range tend to be a lot better at dealing with temperatures in that range.