"Periodically, individual dwarves are struck with an idea for a legendary artifact and enter a strange mood. Dwarves which enter a strange mood will stop whatever they are doing and pursue the construction of this artifact to the exclusion of all else. They will not stop to eat, drink, sleep, or even run away from dangerous creatures. If they do not manage to begin construction of the artifact within a handful of months, they will go insane and die soon afterward…"
From the Dwarf Fortress wiki