Ask HN: What is your favorite TED talk?

I really like Hans Rosling, Clay Shirky, Richard Dawkins, and Nick Bostrom's talks. I've found TED talks to be pretty hit-or-miss, so I'm reaching out to HN.

I'm also aware of this thread: http://www.imminst.org/forum/index.php?showtopic=16384 but I'm more interested in what you guys think.