A good and practical list of 10 angles of attack for understanding a new codebase. More than that, however, I particularly like this bit from the introduction:

When we read our own code, we have a mental model of how things are connected and how they work. When faced with “someone else’s code” we don’t have that. We are faced with pages and pages of code. And often written in a style that is dissimilar to our own.

This can lead us to think that the style of the code is the problem. That if only the style was “correct” (read: like my own) then it would be “easier” to understand.

I want you to put that aside. The fundamental problem with reading someone else’s code is the lack of a mental model. That is neither your fault nor theirs.