The Drs. Iyengar met by chance, at a bus stop in San Francisco when they were graduate students at Stanford. She found him morose and geeky; he thought she was confident, bright and funny. Predictably, they fell in love, and married a few years later, horrifying their families — he is Hindu, she was raised a Sikh — whose respective cultures view arranged marriages as sacrosanct. (Panicked, his mother visited the family astrologer who told her not to fret; the couple had been married in seven past lives and would be married in seven future ones as well.)

It was an involved process, Dr. Garud Iyengar told this reporter later via e-mail, to choose someone outside his caste and his religion. In the end, his marriage calculus was solved by the tricky factor of love. “Over time,” he said, “she became someone I could not live without.”

Explaining romantic attraction, Dr. Sheena Iyengar writes, is nearly impossible. In her book, she relates the experience of one of her graduate students who traveled to India with a woman in whom he had a romantic interest. He knew of the “love on a suspension bridge” study, which showed, through an elaborate ruse, that participants were more likely to develop an attraction for someone they encountered in a dangerous setting, like a spindly bridge swaying above the rapids, than in a more staid environment. The student thought to recreate the study with the object of his affection, on a thrill ride on a rickshaw through Delhi. But it backfired: the woman fell for the rickshaw driver.