Code documentation is one way to share knowledge; clear documentation not only benefits consumers of the library, but also future maintainers. Similarly, implementation comments transmit knowledge across time: you’re writing these comments expressly for the sake of future readers (including Future You!).
> including Future You!
Relevant xkcd, of course: https://xkcd.com/1421/
nb: Randall visited the Goodreads office the day before he put out this comic. As part of the Q&A I asked him what his code comments were like. I.e., I catalyzed this comic 😛!
