Nassim Taleb introduces a three-way distinction that the entire book builds on.

The spectrum he defines:

• Fragile things break under stress and volatility (a wine glass, an over-optimized supply chain)
• Robust things resist stress without being harmed (a rock)
• Antifragile things actually improve from stress, up to a point (muscle tissue, the immune system, certain businesses)

Most people, Taleb argues, only think in terms of the first two categories — but the most interesting and durable systems are the third kind, which genuinely benefit from the right amount of disorder rather than merely surviving it.