My lovely and delightful author friend Melissa McTernan was one of my early readers for Ballad for Jasmine Town, and said recently that she found herself still occasionally thinking about the book, months later. Which to me is such a high compliment! And it has led me to ponder: what is it that makes a story, be it book or show or film, stick in our heads longer than usual?

Plenty of shows or books are perfectly engaging while we’re watching/reading them, but after we’re done, they drop straight...