The achievement of an individual self, a being with a unique past and a trajectory into the future, is one of the glories of human evolution, but it is not without its drawbacks and potential disorders. The price of the sense of an individual identity is a sense of separation from others and nature. Self-reflection can lead to great intellectual and artistic achievement but also to destructive forms of self-regarded and many types of unhappiness. (In an often-cited paper titled “An Wondering Mind Is an Unhappy Mind” psychologists identified a strong correlation between unhappiness and time spent in mind wandering, a principal activity of the default mode network.) But, accepting the good with the bad, most of us take this self as an unshakable given, as real as anything we know, and as the foundation of our life as conscious human beings. Or at least I always took it that way, until my psychedelic experiences led me to wonder.

—Michael Pollan, How to Change Your Mind, Allen Lane, 2018