I felt drowned in pessimism from media, culture, and family for most of my life up to that point, and this book opened up an optimistic perspective on global prosperity, health, violence, education, work, inequality, environment, etc. It makes rational arguments for this general optimism rather than hand-wavey optimism. I think it can be summarized as: "Things aren't so bad for the average human and are improving in most of the important ways. We've hit on patterns (science, markets, etc.) that seem to work, and we should continue to work at making things even better."