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You Will Defend a Choice You Never Made
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The Law Will Not Discount a Fragile Skull
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How Mustard Gas Helped Invent Chemotherapy
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Grab your coffee and let’s dive in.

You're shown two photos of women's faces and asked which one you find more attractive. You point, and the experimenter slides your pick across the table and asks why you chose it. Except that, thanks to a hidden second card and a simple magic trick, it's the face you just rejected. In 2005, Petter Johansson and Lars Hall at Lund University ran this on 120 people, and only 13 percent of the swaps were caught in the moment. The rest of the time, people simply explained themselves. Their reasons were as long and as confident as the ones they gave for real choices, and some praised features that only the rejected photo had. One participant said they chose her because she smiled, while holding a picture of a woman who wasn't smiling.

The team then took the trick to a supermarket. Shoppers in Lund tasted two jams or two teas and picked a favorite, then got a second taste from a jar that had been secretly flipped to serve the one they had turned down. About two-thirds never noticed. Even wildly different pairs, like cinnamon-apple and bitter grapefruit, slipped past most people, who happily described what they loved about the flavor they had rejected. In 2012 the researchers went after something people care about far more than jam. Volunteers in a park filled in a survey on moral issues, and a glued slip on the clipboard reversed two of their answers. Someone who had said government surveillance of email ought to be forbidden now saw that it ought to be permitted, with their own mark beside it. More than two-thirds missed at least one reversal, and about half went on to argue for the view they had just rejected.

Then came an election. In the final stretch of Sweden's 2010 general election, the team asked voters to fill in a questionnaire on issues that split the left and right coalitions, then used sleight of hand to move their answers into the opposite camp. Only one person suspected a trick, and 92 percent accepted the altered answers as their own. Asked again how they planned to vote, one in ten had switched from firm support for one side to the other. None of this makes the volunteers foolish. What the studies suggest is that we often build our reasons after the choice, and from the inside a made-up reason feels exactly like a real one. So a confident explanation, even your own, is weak proof of what actually drove a decision. Next time you hear yourself defending a preference, a survey answer, or even a vote, it's worth a moment's doubt about whether you're describing the choice or just defending the one you're holding.

On February 20, 1889, in the high school of the village of Waukesha, Wisconsin, George Putney, a boy of about eleven, sat across the aisle from Andrew Vosburg, who was about fourteen. After the class had been called to order, Putney reached over and touched Vosburg's right shin with his toe. The contact was slight, and Vosburg barely felt it at first, but then the pain arrived. On New Year's Day he had hurt the same leg in a sledding accident, just above the knee, and that injury was still healing. In the days that followed he was in severe pain, the shin swelled, and he vomited. Surgeons later found the bone itself beginning to come apart. The court would record that he would never recover the use of the limb.

Vosburg's family sued for assault and battery. Putney had not meant to cause a serious injury, and he did not know about the weakened leg. In 1891 the Wisconsin Supreme Court still held that he could be responsible for the whole result. A kick in a classroom after lessons had started was an unlawful act, a breach of school order. The same touch on the playground might have been treated as ordinary play, because children at recess have an implied license to jostle one another. Once the classroom act was wrongful, the boy who did it was liable for the injury that followed in a natural sequence, even if no one could have seen it coming. Liability did not depend on how hard Putney had kicked. Once the classroom touch was proved unlawful, it carried the full bodily consequences that actually followed. Later lawyers gave the idea a plainer name: the eggshell-skull rule, or the rule that you take the victim as you find them. A hidden weakness in the person you wrong does not cut your liability down to the harm a sturdier body would have suffered.

The same principle now reaches beyond intentional blows into ordinary negligence. If a light collision or a minor blow finds a hidden weakness, the damage may be out of all proportion to the force. The person who caused the contact still pays for the full injury, not a discounted version sized to an average skull or an average shin. The defendant need not have known about the weakness. Vosburg remains a standard example in American law teaching, and the same idea now sits in negligence as well as in battery. The court refused to shrink the wrong just because the boy who received it was already fragile. Putney was held for the injury that followed from that slight classroom touch, including the harm that came of a leg already weakened by the earlier sledding accident.