Supernatural and Don Quixote (spoiler alert)

One of my favorite television shows is the contemporary fantasy Supernatural. I've spent the break between semesters catching up on season 10. The show is littered with references to pop culture icons, usually celebrities, music, or film. Needless to say, I was surprised but delighted when a Don Quixote reference showed up in episode 18.

I admit that I did not get the reference at first. And I've already spoiled it for you that this is a reference to Don Quixote. But let's see if you can match the following quote with the character, or describe the context in which it takes place: "What is the maddest thing a man can do?"

Of course, you can always watch the episode to find out!