School leaders: What’s the best book about (or related to) leadership that you’ve ever read?

For an upcoming Edutopia article, I'm looking for book recommendations—and 1-2 key insights from your book of choice—that you've applied to school leadership/education.

I'm compiling responses and insights and will be summarizing them, similar to this Edutopia article where I asked 10 school leaders about the one piece of advice they'd give their younger selves. Thanks so much!