Harari's two previous books--Sapiens (which explored our past) and Homo Deus (which considered our potential future based on current developments)--are exceptional detailed looks at a wide range of topics. In 21 Lessons for the 21st Century, he breaks down these broader themes into digestible chapters that are practical, relevant, and compelling.Many of the ideas here are ones explored in his previous works, though I found reviewing them again helpful and reinforcing; they also allow new readers to understand his theories without having to work through his previous books (which interested readers should do anyway). In addition, he organizes these ideas into five broad themes--the technological challenge, the political challenge, despair and hope, truth, and resilience--and each chapter has both a title (e.g., "Liberty") and a core concept (e.g., "Big Data is Watching You"). Harari often does a nice job tying one chapter into the next, making the entire work a cohesive argument instead of a series of unrelated musings.Harari writes from an authoritative position not because he earned a doctorate in history from Oxford, but because he's thoughtful, insightful, well-read, and relies on the scholarship of many others. He has the ability to construct powerful arguments through research, history, philosophers, cultural study, and his own insights and analysis, and he is quite willing to suggest flaws in the arguments of groups on both sides of any issue--religious, political, nationalistic, cultural, etc. But what I most appreciate about this is his repeated admonition that we don't know as much as we think we do. This allows him to take a "guide on the side" stance instead of being a "sage on the stage," and the reader is therefore challenged to consider the arguments and find points of agreement or disagreement.So yes, there are areas where a reasonable person could disagree with Harari in terms of content and presentation. At one point he argues that since all experiences are self-created, "Whatever you can feel in Fiji, you can feel anywhere in the world." I believe some experiences are so unique to setting and context that they'll only occur in that specific setting (including not only Fiji, but seeing "Raiders of the Lost Ark" on the big screen or attending a Bruce Springsteen concert). His section on "Despair and Hope" is heavy on despair and light (perhaps absent) of hope, and his section on Resilience focuses more on the challenges we face than how we may overcome them.In fact, Harari offers little in the way of "solutions" to the numerous problems he describes. Interestingly, his closing the book with Meditation suggests this is the closest thing he has to an answer, and in a sense this is correct; given his emphasis on awareness of our challenges, the practice of paying attention is critical. However, he describes meditation as a method to alleviate personal suffering by recognizing that all experiences are self-created because there's no objective truth, and the implication seems to be that alleviating suffering is thus a central goal. This doesn't mean we should focus on relieving the suffering of others, as he shares an anecdote of a person saying his purpose in life was to help others, but "what I still haven't figured out is why the other people are here." Does Harari believe that if everyone relieved personal suffering they'd be happy? Does it matter if there's no broader meaning to life in terms of our happiness, when lots of research indicates a sense of meaning and purpose is what makes us happiest? Is it a goal of life to be happy, or just to exist until we don't exist anymore? He might have answered this by simply explaining why he dedicated so much time to researching and writing this book (and his others). Understanding what motivated him to take on this task could have shared some insight into how he personally finds meaning and purpose in life, which would have added some nice context to his outstanding work. Sadly, that's missing.