When my 7-year-old twin boys were first learning to play piano, I would check in with them regularly to see if they were still enjoying it. Finally, their teacher—a Russian woman who was evidently unfamiliar with fashionable theories of child rearing—told me that if I wanted my kids to learn an instrument, I needed to cut it out.

“Some weeks they won’t like it,” she said. “So what? Stop asking.”

Experts...