Unlike the United States, Thailand does not have four seasons. Instead, it has a "hot" or "rainy" season, both of which will feel hot to a foreigner who is not from the Equator! Due to this different environment, Thais have adapted differently and learned to live with this type of environment.
The relatively little change to the environment year-round is one reason why this part of the world is so biodiverse. Plant and animal species have adapted for centuries without needing to travel with the weather, change their habits, or change any innate characteristics, so there are now many unique species here ranging from insects to monkeys. There are also many natural river ways in Thailand.
The most wonderful part of this environment that helps people live here is the abundance of edible plants that grow just about everywhere year-round. I mentioned the diversity of fruits here before, yet I am still so amazed how often I walk by a banana, papaya or coconut tree! There is also a lot of aquatic food and life. The river system acts as a transportation system which people have used for centuries to travel and thus trade and build civilization. Even today, many Thais will travel by boat within their communities.