I referenced this video in a discussion the other day about the Conada effect and how wings work [1], and I thought the video was so good it merited its own thread. Feynman gives a supremely insightful answer to a superficially simple question, and I think the issue that he discusses is at the heart of many disagreements, especially on internet forums.
[1] https://news.ycombinator.com/item?id=8470234
* edit: rewording for clarity