When the thugs arrive — the Nazis and the Ku Klux Klan — who stands up to them? That’s a question raised by Rutger Bregman in his new book, Moral Ambition. Bregman, who is Dutch, was fascinated by the example of Nieuwlande, a tiny Dutch town whose residents concealed almost 100 Jews from the Nazi occupiers. “The concentration of people in hiding was higher than nearly everywhere else in Europe.”

So what made the citizens of Nieuwlande courageous? Psychologists have examined the determinants of such heroism. One influential study was conducted by Pearl and Samuel Oliner, authors of The Altruistic Personality: Rescuers of Jews in Nazi Europe and founders of the Altruistic Personality Institute. The Oliners interviewed hundreds of people who had protected Jews in Europe during the second world war. One can understand Sam Oliner’s interest in the topic: he was Jewish, born in Poland in 1930, lost his entire family and, at the age of 12, was hidden from his would-be murderers by a sympathetic Catholic peasant.

A similar project was conducted by psychologist Eva Fogelman, author of Conscience and Courage: Rescuers of Jews during the Holocaust. And yet, says Bregman, these studies of heroic acts don’t find many indicators of a heroic personality type.