It was long overdue, but I finally finished reading The Innovator's Dilemma by Clayton Christensen, an HBS professor. So many people kept citing this work around me, and I now understand why. The book is a bit slow and dry in its writing style, but the key points are incredibly deep, thought-provoking, and not as often discussed in start-up pop culture.
My biggest takeaway is that when companies are doing the "right" things, like being good managers, following business school teachings, executing, listening to customers, etc., these practices that help them scale successfully are exactly the WRONG things to be doing when confronted with disruptive innovation. That's the core of the dilemma. As a start-up gets traction and grows into a big company, it makes it much less likely that it will be able to keep doing disruptive innovation. This is a really interesting concept, and one that's bittersweet.
My notes are below. You can also download a great book guide that was included in the book at the bottom of this post (sorry for the quality, I took the photos on my phone).
I really enjoyed the book, even though it took me a while to get through it (this was a physical copy I was reading for 10-20 pages at a time).
Part 1: Why great companies can fail
Ch. 1: How can great firms fail