On LessWrong and elsewhere in the Rationalsphere, it seems like there's more focus on the theoretical and philosophical aspects of rationality than on the concrete, actionable, and applied aspects of rationality. I know this isn't always the case; thank you CFAR and others for existing, but I think learning more about the practiced craft of rationality and how individuals in our community have improved their lives in significant ways because of specific decisions, events, or actions is a good idea, thus this question.
Answers don't have to be related to applied rationality, though I definitely want to hear such answers if your experience of life improvement was derived from rationality in some way.
I'll get started:
The distinction between maps and the territory and related discussions that I learned about / read improved my ability to navigate complex layers of abstractions in technical systems, which resulted in me becoming better at IT related problem solving than I was prior to learning about / reading those things. I believe that this improvement came about because the idea of maps not being the territory helped me shred through the illusions surrounding computer systems: these systems were created by people, the creation and implementation of those systems was shaped by underlying constraints imposed by reality, and those systems' inner workings could be pinned down and understood by deconstructing the maps used to explain them / mythologize them (a not insignificant amount of people think that "being good with computers" is a magical / mystical thing; this is anecdotal data from my own experience fixing computers for people over the past 6 years.). Learning about the distinction between maps and the territory was and still is an extremely value-congruent action, because I value pursuing and achieving truth and understanding for any and all given topics, so I'm glad I read about that distinction and read the discussions around it.
I should note that I didn't deliberately set out to read about the "map and territory" distinction, rather, it was something I came across while reading The Sequences and generally around LessWrong. Furthermore, I think my above claim regarding learning about that distinction and the resulting benefits might be on shaky ground, because while I'm reasonably epistemically confident in that claim, it's very possible this is just hindsight bias. However, I've been able to help others better understand computers and other technical / complex systems via informing them of the "map and territory" distinction, so it seems like there's some credence to my claim. Those interactions with others and my own experiences with the "map and territory" distinction are why I believe learning about that distinction was helpful in the specific ways I mentioned. (I think it's been helpful in other ways too, but the above is what I'm mentioning for now)
What specific thing improved your life?