The Mythical Man-Month is a collection of essays that generalize some "rules" about software engineering: adding engineers to a project, "no silver bullets" to 10x productivity, importance of communication in a big project, etc. I loved reading it, partly because I could relate/empathize with so many of the ideas.

TMM-M is like a philosophy book, with clearly laid out observations and evidence behind the wisdom Spoiler: not all the observations hold up! There are many things still true 40+ years after it was first published; but it's also fun to read about the observations that don't hold up today (...although the 20th anniversary Chapter 19 revisits all of the concepts in retrospect). I can definitely see myself rereading and referencing this book in the future!