You understand your coworkers' PRs as thoroughly and intuitively as they do? Any significant PR will contain things you don't even notice or think to ask about. And the answers to the questions you do ask are the end result of a thought process you didn't go through and therefore also don't understand as deeply.

Back to the novel analogy, you could ask an author why he incorporated this or that character trait or plot point, but all the explanation in the world will not make you able to write the next chapter as well as he could.