How to dissect a query to learn more about the optimizer

I recently came across this web presentation on Jonathan Lewis' blog in this post. It is a great presentation from my favorite expert on Oracle. I really admire the way Jonathan is able to see how the optimizer works, underneath the SQL, like Neo in the movie: The Matrix. As already noted in the title of this post, the presentation is about dissecting one query to see how much you can learn about how the optimizer works, and how you have to think when dealing with a difficult problem in SQL.