Easy-going introduction to FIRE (Financial independence, retire early). Although each individual chapter was obvious, it was interesting to pull them together. In particular, the idea that the % of your income that you save determines when you become financially independent. Apparently some people hit 90%, which means they get 9 years of retirement for each year worked. No-one had ever explained it that way. In general, Roth is much more focused on frugality as a route to independence instead of investment returns.
The chapter on working out what you want is probably the most important and least well-developed. If your life-goal is to pirate media and eat beans for the rest of your life, then you'll become independent fast. But I'm not sure that's a life worth living. Equally if you follow untrammeled consumerism, you'll be working for a very long time. My inclination is much more towards the legume life, and I have to will myself to break out of it. Still, there's a lot to be said for paid side projects, cheap hobbies, and work travel. Right now, my goal would be to have a second home somewhere quiet full of bikes and books that friends and family could stay at, and then have (rent?) somewhere small-ish in the city that I work. But before that, I'll keep traveling and saving.