Sometimes advice isn’t just bad. It’s delusional.

That’s what Jean Twenge writes in her new book, Generations: The Real Differences Between Gen Z, Millennials, Gen X, Boomers, and Silents—and What They Mean for America’s Future. She makes this comment about “the most optimistic and self-confident generation in history.” My generation. The Millennials.

Here’s the advice we heard over and over growing up: “just be yourself,” “believe in yourself and anything is possible,” “express yourself,” and “you have to learn to love yourself before you can love someone else.” Her counterpoint: what if you’re a jerk? Or even a serial killer? No, not anything is possible. You’re delusional. She writes, “People who really love themselves are called narcissists, and they make horrible relationship partners.”

That's tough medicine for us Millennials! But she’s right. I felt understood in this book. And it helped me to understand other generations both older and younger. Because in many ways we have less in common with each other than ever before. Dr. Twenge, writes, “The breakneck speed of cultural change means that growing up today is a completely different experience from growing up in the 1950s or the 1980s—or even the 2000s.”

Twenge is a professor of psychology at San Diego State University and widely published researcher. The book is full of important insights. She describes same-sex marriage as the most rapid change of public opinion on a social issue in history. Not coincidentally, she says all signs point to further retreat from religion. In place of religion we get politics. She warns, “World history suggests that transferring religious beliefs into politics will not end well.”

I had to agree with her sense that optimism has been lost in the United States since the Great Recession. And that our society—built on abstract ideas—depends on trust and truth that we don’t often enjoy today.

Generations is a bracing book, and an important one, whether you’re a parent or pastor or politician or just want to learn more about yourself and your neighbors. Jean joined me on Gospelbound to discuss how generational differences might be shaping America's future, why technology isn't all bad, and more.