Taleb coined the word “antifragile” to describe things that actually need to get knocked over now and then in order to become strong. I used the word “things,” but there are very few inanimate objects that are antifragile. Rather, antifragility is a common property of complex systems that were designed (by evolution, and sometimes by people) to function in a world that is unpredictable.[11] The ultimate antifragile system is the immune system, which requires early exposure to dirt, parasites, and bacteria in order to set itself up in childhood.