What’s the most consistently insightful book you read (any genre)?

Whether it’s fiction or non-fiction, and no matter the topic, what book made you think “wow, the author is really insightful” in terms of observations, analyses, or ideas?

This doesn’t necessarily have to be the book that gave YOU the most insights, because even a straight-forward fact-presenting book can make your gears turn. I’m curious about the AUTHOR being the source of insightful ideas.