Dunno about people in general but I build up a tolerance to chilli surprisingly quickly. It's not about eating super hot things, but about eating things with a nice warmth on a regular basis. Over the course of a month I can go from "jalapenos are hot" to "a forkful of habanero is nice" with little increase in subjective heat, and then if I stop eating spicy food for a couple of weeks it'll reset back to the start.