Chapter 1 The Untruth of Fragility: What Doesn''t Kill You Makes You Weaker When heaven is about to confer a great responsibility on any man, it will exercise his mind with suffering, subject his sinews and bones to hard work, expose his body to hunger, put him to poverty, place obstacles in the paths of his deeds, so as to stimulate his mind, harden his nature, and improve wherever he is incompetent. meng tzu (mencius), fourth century BCE In August 2009, Max Haidt, age three, had his first day of preschool in Charlottesville, Virginia. But before he was allowed to take the first step on his eighteen-year journey to a college degree, his parents, Jon and Jayne, had to attend a mandatory orientation session where the rules and procedures were explained by Max''s teacher. The most important rule, judging by the time spent discussing it, was: no nuts. Because of the risk to children with peanut allergies, there was an absolute prohibition on bringing anything containing nuts into the building. Of course, peanuts are legumes, not nuts, but some kids have allergies to tree nuts, too, so along with peanuts and peanut butter, all nuts and nut products were banned. And to be extra safe, the school also banned anything produced in a factory that processes nuts, so many kinds of dried fruits and other snacks were prohibited, too. As the list of prohibited substances grew, and as the clock ticked on, Jon asked the assembled group of parents what he thought was a helpful question: "Does anyone here have a child with any kind of nut allergy? If we know about the kids'' actual allergies, I''m sure we''ll all do everything we can to avoid risk.

But if there''s no kid in the class with such an allergy, then maybe we can lighten up a bit and instead of banning all those things, just ban peanuts?" The teacher was visibly annoyed by Jon''s question, and she moved rapidly to stop any parent from responding. Don''t put anyone on the spot, she said. Don''t make any parent feel uncomfortable. Regardless of whether anyone in the class is affected, these are the school''s rules. You can''t blame the school for being so cautious. Peanut allergies were rare among American children up until the mid-1990s, when one study found that only four out of a thousand children under the age of eight had such an allergy (meaning probably nobody in Max''s entire preschool of about one hundred kids). But by 2008, according to the same survey, using the same measures, the rate had more than tripled, to fourteen out of a thousand (meaning probably one or two kids in Max''s school). Nobody knew why American children were suddenly becoming more allergic to peanuts, but the logical and compassionate response was obvious: Kids are vulnerable.

Protect them from peanuts, peanut products, and anything that has been in contact with nuts of any kind. Why not? What''s the harm, other than some inconvenience to parents preparing lunches? But it turns out that the harm was severe. It was later discovered that peanut allergies were surging precisely because parents and teachers had started protecting children from exposure to peanuts back in the 1990s. In February 2015, an authoritative study was published. The LEAP (Learning Early About Peanut Allergy) study was based on the hypothesis that "regular eating of peanut-containing products, when started during infancy, will elicit a protective immune response instead of an allergic immune reaction." The researchers recruited the parents of 640 infants (four to eleven months old) who were at high risk of developing a peanut allergy because they had severe eczema or had tested positive for another allergy. The researchers told half the parents to follow the standard advice for high-risk kids, which was to avoid all exposure to peanuts and peanut products. The other half were given a supply of a snack made from peanut butter and puffed corn and were told to give some to their child at least three times a week.

The researchers followed all the families carefully, and when the children turned five years old, they were tested for an allergic reaction to peanuts. The results were stunning. Among the children who had been "protected" from peanuts, 17% had developed a peanut allergy. In the group that had been deliberately exposed to peanut products, only 3% had developed an allergy. As one of the researchers said in an interview, "For decades allergists have been recommending that young infants avoid consuming allergenic foods such as peanut to prevent food allergies. Our findings suggest that this advice was incorrect and may have contributed to the rise in the peanut and other food allergies." It makes perfect sense. The immune system is a miracle of evolutionary engineering.

It can''t possibly anticipate all the pathogens and parasites a child will encounter-especially in a mobile and omnivorous species such as ours-so it is "designed" (by natural selection) to learn rapidly from early experience. The immune system is a complex adaptive system, which can be defined as a dynamic system that is able to adapt in and evolve with a changing environment. It requires exposure to a range of foods, bacteria, and even parasitic worms in order to develop its ability to mount an immune response to real threats (such as the bacterium that causes strep throat) while ignoring nonthreats (such as peanut proteins). Vaccination uses the same logic. Childhood vaccines make us healthier not by reducing threats in the world ("Ban germs in schools!") but by exposing children to those threats in small doses, thereby giving children''s immune systems the opportunity to learn how to fend off similar threats in the future. This is the underlying rationale for what is called the hygiene hypothesis, the leading explanation for why allergy rates generally go up as countries get wealthier and cleaner-another example of a problem of progress. Developmental psychologist Alison Gopnik explains the hypothesis succinctly and does us the favor of linking it to our mission in this book: Thanks to hygiene, antibiotics and too little outdoor play, children don''t get exposed to microbes as they once did. This may lead them to develop immune systems that overreact to substances that aren''t actually threatening-causing allergies.

In the same way, by shielding children from every possible risk, we may lead them to react with exaggerated fear to situations that aren''t risky at all and isolate them from the adult skills that they will one day have to master [emphasis added]. This brings us to the oracle''s first Great Untruth, the Untruth of Fragility: What doesn''t kill you makes you weaker. Of course, Nietzsche''s original aphorism-"What doesn''t kill me makes me stronger"-is not entirely correct if taken literally; some things that don''t kill you can still leave you permanently damaged and diminished. But teaching kids that failures, insults, and painful experiences will do lasting damage is harmful in and of itself. Human beings need physical and mental challenges and stressors or we deteriorate. For example, muscles and joints need stressors to develop properly. Too much rest causes muscles to atrophy, joints to lose range of motion, heart and lung function to decline, and blood clots to form. Without the challenges imposed by gravity, astronauts develop muscle weakness and joint degeneration.

Antifragility No one has done a better job of explaining the harm of avoiding stressors, risks, and small doses of pain than Nassim Nicholas Taleb, the Lebanese-born statistician, stock trader, and polymath who is now a professor of risk engineering at New York University. In his 2007 best seller, The Black Swan, Taleb argued that most of us think about risk in the wrong way. In complex systems, it is virtually inevitable that unforeseen problems will arise, yet we persist in trying to calculate risk based on past experiences. Life has a way of creating completely unexpected events-events Taleb likens to the appearance of a black swan when, based on your past experience, you assumed that all swans were white. (Taleb was one of the few who predicted the global financial crisis of 2008, based on the financial system''s vulnerability to "black swan" events.) In his later book Antifragile, Taleb explains how systems and people can survive the inevitable black swans of life and, like the immune system, grow stronger in response. Taleb asks us to distinguish three kinds of things. Some, like china teacups, are fragile: they break easily and cannot heal themselves, so you must handle them gently and keep them away from toddlers.

Other things are resilient: they can withstand shocks. Parents usually give their toddlers plastic cups precisely because plastic can survive repeated falls to the floor, although the cups do not benefit from such falls. But Taleb asks us to look beyond the overused word "resilience" and recognize that some things are antifragile. Many of the important systems in our economic and political life are like our immune systems: they require stressors and challenges in order to learn, adapt, and grow. Systems that are antifragile become rigid, weak, and inefficient when nothing challenges them or pushes them to respond vigorously. He notes that muscles, bones, and children are antifragile: Just as spending a month in bed . leads to muscle atrophy, complex systems are weakened, even killed, when deprived of stressors. Much of our modern, structured, world has been harming us with top-down policies and contraptions .

which do precisely this: an insult to the antifragility of systems. This is the tragedy of modernity: as with neurotically overprotective parents, those trying to help are often hurting us the most [emphasis added.