Each year millions and millions of whatever currency you’d care to have are spent explaining generations to one another. Inherent in that expensive explantation is the idea that people born at about the same time are basically alike, and very different from people born at other times.

But, as Bobby Duffy explains in his book The Generation Myth: Why When You’re Born Matters Less Than You Think, while this can be the case, it ain’t always necessarily so. Generational identities are not fixed, but fluid. They change over time. And beware of those who try to sell you simplistic—or simply false–concepts like generational warfare, or inevitable social decline; that only the kids care about the environment, or that Gen Z is “the suicidal generation”.

Bobby Duffy is Professor of Public Policy and Director of the Policy Institute at King’s College London. Formerly director of research at the public opinion firm Ipsos MORI, his most recent book was published in the United States under the title Why We’re Wrong About Nearly Everything.