There is certainly a reputation that Thai food is hot. What is not well understood though is that there are lot of choice available in terms of the level of heat. Thais themselves do not all like the same level of heat, there are even a proportion who don't eat hot at all.
When you are ordering food in Thailand you specify how hot you want the dish (if it is a dish with chilis). So when you cook Thai food at home it is up to you to add as much chili as you want yourself. As you eat hot food you build up a tolerance to it, and you learn to appreciate it as a flavour, rather than as a hindrance to flavour which is what happens when you eat food that is too hot for you.