Sheena Iyengar is the psychologist responsible for the famous jam experiment. You may have heard about it: At a luxury food store in Menlo Park, researchers set up a table offering samples of jam. Sometimes, there were six different flavors to choose from. At other times, there were 24. (In both cases, popular flavors like strawberry were left out.) Shoppers were more likely to stop by the table with more flavors. But after the taste test, those who chose from the smaller number were 10 times more likely to actually buy jam: 30 percent versus 3 percent. Having too many options, it seems, made it harder to settle on a single selection.

Wherever she goes, people tell Iyengar about her own experiment. The head of Fidelity Research explained it to her, as did a McKinsey & Company executive and a random woman sitting next to her on a plane. A colleague told her he had heard Rush Limbaugh denounce it on the radio. That rant was probably a reaction to Barry Schwartz, the author of “The Paradox of Choice” (2004), who often cites the jam study in antimarket polemics lamenting the abundance of consumer choice. In Schwartz’s ideal world, stores wouldn’t offer such ridiculous, brain-­taxing plenitude. Who needs two dozen types of jam?

“The study hardly seems mine anymore, now that it has received so much attention and been described in so many different ways,” Iyengar, a professor at Columbia Business School, writes in “The Art of Choosing.” “From the various versions people have heard and passed on,” she adds, “a refrain has emerged: More is less. That is, more choice leads to less satisfaction or fulfillment or happiness.”

Now Iyengar is having her own say about the jam experiment and the many other puzzles and paradoxes of choice. More choice is not always better, she suggests, but neither is less. The optimal amount of choice lies somewhere in between infinity and very little, and that optimum depends on context and culture. “In practice, people can cope with larger assortments than research on our basic cognitive limitations might suggest,” Iyengar writes. “After all, visiting the cereal aisle doesn’t usually give shoppers a nervous breakdown.”