In director Rob Reiner’s 1987 fairy-tale film The Princess Bride, one of the characters engages in a battle of wits against the protagonist. At one point, he exclaims, “You fell victim to one of the classic blunders! The most famous of which is ‘never get involved in a land war in Asia.’ ” I think we can all agree that recent history has shown this statement to be good advice. The famous mathematician and philosopher Bertrand Russell suggested another tip to those who want to make sure they avoid fanaticism: “Do not feel absolutely certain of anything.” The examples in this book demonstrate that this “commandment” can also be taken as a useful hint for how to dodge major blunders—but I am not absolutely certain about this . . . While doubt often comes across as a sign of weakness, it is also an effective defense mechanism, and it’s an essential operating principle for science.

Kelvin, Hoyle, and Einstein revealed yet another fascinating side of human nature. Just as people (scientists included) are sometimes reluctant to admit their mistakes, they also on occasion stubbornly oppose new ideas. Max Planck, one of the forefathers of quantum mechanics, once remarked cynically, “New scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.” This may be sad but true.

Psychologists Amos Tversky and Daniel Kahneman established a cognitive basis for common human errors using the concept of heuristics: simple rules of thumb that guide decision making. One of their findings was that people tend to rely more on their intuitive understanding—which is based largely on their personal experience—than on actual data. Naturally, scientists of the caliber of Darwin, Pauling, or Einstein believed that their intuition would guide them to the correct answer even when the right way forward was elusive or when the scientific landscape was changing at a bone-breaking pace. As I have noted above, Bertrand Russell understood the dangers of overconfidence and certainty, and he thought that he had found a solution when he advocated a habit of hinging beliefs “upon observations and inferences as impersonal, and as much divested of local and temperamental bias, as is possible for human beings.” Unfortunately, it is not easy to follow this advice. Modern neuroscience has shown unambiguously that the orbitofrontal cortex (a region in the frontal lobes in the brain) integrates emotions into the stream of rational thought. Humans are not purely rational beings capable of completely turning off their passions.

Despite their blunders, and perhaps even because of them, the five individuals I have followed and sketched in this book have produced not just innovations within their respective sciences but also truly great intellectual creations. Unlike many scientific works that target only professionals from within the same discipline as their audience, the oeuvres of these masters have crossed the boundaries between science and general culture. The impact of their ideas has been felt far beyond their immediate significance for biology, geology, physics, or chemistry. In this sense, the work of Darwin, Kelvin, Pauling, Hoyle, and Einstein comes closer in spirit to achievements in literature, art, and music—both cut a broad swath across erudition.

There is no better way to end a book on blunders than with an important reminder—a plea for humility, if you like—that nobody can express more eloquently than Darwin: