I was a graduate student living on 20-25k/year and I liked embracing the idea that this lifestyle is not only sufficient, but actually luxurious. Also some things resonated with my values and upbringing, such as the idea of using money where it matters, on travel, time with loved ones, and valued hobbies/self-improvement, instead of using it on stuff and laziness. The environmental message, of these costly habits also being environmentally wasteful, also resonated. Finally, I liked the idea of FI, as a matter of security, although I'm not currently sold on the "RE" part of the equation. At least not "RE in 10 years". Love the idea of FI in 10 years, though, and not being *dependent* on the job for basic living expenses. Oh, another idea that was novel and stuck with me: how having money in the bank allows you better financial choices, like dropping comprehensive car insurance or having a high-deductible health plan.
I guess basically it just made sense to me an a fundamental level. I feel like I tend toward being a natural saver psychologically, but reading MMM gave that more focus and justification and motivation. Not saying I'm perfect now, in fact I have a fair bit to work on, but it definitely feels like moving the right direction in terms of my values, and accomplishing frugality goals or taking time to enjoy frugal pleasures makes me genuinely happy. Whereas getting a new phone and computer last fall generated some guilt and doubt.