Apparently this quotation from General Baron Kurt von Hammerstein-Equord is well-known, but I just came across it for the first time (in one of the latest Ender books):
I divide officers into four classes – the clever, the lazy, the stupid, and the industrious. The man who is clever and lazy is fit for the very highest commands. He has the temperament and the requisite nerves to deal with all situations. Those who are clever and industrious are fitted for the high staff appointments. Use can be made of those who are stupid and lazy. But whoever is stupid and industrious must be removed immediately.
Turns out there’s dispute both as to the authenticity and as to the precise wording of the quotation. But it’s a great line in any case.