Bought bitcoin early 2018 for the first time right before it dropped faster than I could sell, lol. Then I didn't care anymore and forgot about it. Regained interest when someone casually mentioned it and I noticed it was now at 20k at the end of 2020. Fell down the bitcoin rabbit hole shortly after.
Honorable mentions: The Bitcoin Standard, What Bitcoin Did, What is Money, Mastering Bitcoin, The Internet of Money, Mastering the Lightning Network