Much of Buddhism can be boiled down to a bad-news/good-news story. The bad news is that life is full of suffering and we humans are full of illusions. The good news is that these two problems are actually one problem: If we could get rid of our illusions—if we could see the world clearly—our suffering would end.

And there’s more good news: Buddhism offers tools for doing that job. A good example is the type of meditation known as mindfulness meditation, now practiced by millions of people in the U.S. and other places far from...