"Ok, so the client contacts the server and receives the result, but half of the result is missing, so...."
"Well, actually, the client uses DNS to look up the server's address first."
"Ok, thanks. Now I know."
A well-done well-actually is a brilliant demonstration of superiority.
There is no hard-and-fast rule for figuring out what is and is not a well-actually, but the biggest factors (at least for me) are (1) did it derail the conversation, (2) did my correcting someone make it less acceptable to not know something, and (3) was my motivation to do something like show off?
I've been guilty of all 3. Anecdotally, I found that the effect of this lightweight rule was that at HS it was very much ok to not know something, and let me tell you, adjusting to the real world, where that is subtly untrue, is a trial.
As for the "parachuting in" problem, that's essentially the gist of a different lightweight social rule, "no backseat driving". :)
Hallelujah! Someone who understands! :-) [1]
I've done it as well, and I hate it when I realize I am.
I suspect the worse part of HS' policies is exactly that "adjusting to the real world, where [it was very much ok to not know something] is subtly untrue, is a trial." In the typical business environment, appearing not to know something is a very unsubtle weakness.
[1] I'm completely unrelated to Hacker School.
It looks immensely easy to fall into a trap of caring too much about the rules and not caring enough about the code, and I can imagine a large group of people trying to play along rather than try to become better "hackers". "Ohh, I'm sorry, you did actually just save us from three hours of bashing our head into a wall by recommending a specific algorithm, but you also broke the rules. For shame!"