A tough manager will have realistic quotas for his employees that he keeps to himself and aggressively stretch quotas, anywhere from ten percent higher to a lot more, which he imposes on his staff. If his people miss the stretch numbers but exceed the realistic goals, he's happy. If he's a superb manager, he knows how far they can stretch without breaking.

The Creative Habit: Learn It and Use It for Life (ed. Simon and Schuster, 2003)