The important thing is not to shout at this point, Vimes told himself. Do not ... what do they call it ... go spare? Treat this as a learning exercise. Find out why the world is not as you thought it was. Assemble the facts, digest the information, consider the implications. Then go spare. But with precision.
[I have had cause to apply this one recently. It particularly resonated to see it in the book just now.]
For the benighted Yanks among us:
(The secondary Wiktionary definition doesn't seem to convey the depth of anger that Urban Dictionary and various citations I looked at did.)
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).