in reply to "The Work of a Stranger ..."
On the same point ... I just had to dive into a logic problem in a twelve-year old application that I wrote.
I was deathly afraid to touch it. Because the logic is complex and, although I understood the ins-and-outs of the thing at that time, I had long since forgotten everything about it. (I even found myself grepping for the location of key subroutines.)
I was able to “bootstrap” back into that zone and to resolve the problem because of the application-specific knowledge that was embedded in those copious and detailed comments throughout the code. At the time that I originally wrote the logic, and of course then understood what I was doing perfectly, I wrote paragraphs of comments and kept them. What had become over time obtuse and arcane once again became clear.