Code isn't a book. The quote you call into question is semi-famous and I believe the idea is that it's relatively difficult to jump into one code unit of a lar

Code isn't a book. The quote you call into question is semi-famous and I believe the idea is that it's relatively difficult to jump into one code unit of a larger system and get back up-to-speed because one must fill the data cache of their brain with all the considerations for why the author may have done things in a certain way. The algorithm choices and edge cases and exceptional logic paths were clearer to the one writing the original at the time.