Nicholas Nassim Taleb writes a lot of good books. This is one of them. In Antifragile, Taleb tries to push one central idea: The difference between Fragile and Antifragile Systems. Antifragile systems learn and improve over time. They use small errors to get better and disarm the harmful effects of black swans.
Expanding on the idea of Chaotic Systems that exhibit black swan events, he detailed in his other book The Black Swan, he builds the idea of "Antifragility". Antifragile systems are natural, because nature is unpredictable and has black swan mechanics built in, hence natural systems adapted to these circumstances, due to Evolution.
These systems are messy, self-reinforcing, healing and complex. It's very hard to understand them with mathematical analysis, they are often fractal in nature. Nobody knows and really understands how Paris is fed every day, yet it happens, effortlessly, with a relatively high resistance to shocks, changing food prices and such. The system is resilient, because it grew on it's own. It's antifragile. A planned economy, like those seen in the Soviet Union, is the opposite, it's fragile.
Fragile Systems on the other hand, are often humanly designed, they don't show self-healing, self-repairing properties. They rarely exhibit small mistakes, from which they could improve. Instead they build up large internal risks and stresses and then collapse all of a sudden, without much of a prior warning. They are ill adapted to the natural world and the black swan events that happen within it from time to time. Fragile Systems are rigid and stiff, not bendable like a piece of living wood, but more like a piece of ceramics, that snaps when put under too much pressure.
The main takeaway from the book is this distinction, and how it makes sense to keep it in mind when thinking about the world and how it works.
Because a lot of systems, that are human built (especially the financial system and companies) are as of now, fragile and could be completely broken in case of a particularly bad black swan event. Instead, Taleb argues, we should focus on building systems that are more resilient in the face of failure, systems that give and bend more, and adapt to changing circumstances.
In short we need antifragile systems, which gain from chaos and disorder, improving over time, adapting to the changing world.