When I was in law school, I devised my own idiosyncratic solution to the problem of studying a topic I knew nothing about. I'd wander into the library stacks, head to the relevant section, and pluck a book at random. I'd flip to the footnotes, and write down the books that seemed to occur most often. Then I'd pull them off the shelves, read their footnotes, and look at those books. It usually took only 2 or 3 rounds of this exercise before I had a pretty fair idea of who were the leading authorities in the field. After reading 3 or 4 of those books, I usually had at least enough orientation in the subject to understand what the main questions at issue were - and to seek my own answers, always provisional, always subject to new understanding, always requiring new reading and new thinking.

--David Frum

The oldest (non-dead) source I could find was this 2008 post by someone else quoting Frum.

Related to: Update Yourself Incrementally and For progress to be by accumulaton and not by random walk, read great books