Terry Pratchett. The Thief Of Time (№ 386065)

In General, human beings should pay tribute. They had a very strange feature in the universe. Even her grandfather had often noted it. No other species on the Flat world and couldn't think of boredom. Perhaps it is boredom, not mental development, forced people to climb the ladder of evolution. Trolls and dwarves also have acquired this strange ability to look at the universe and think, "Oh, same as yesterday, how dull. I wonder what would happen if I crack a stone out of the head?"