On reflection I feel that I should be more specific. Your dwarves need many things in order to stay happy and emotionally balanced. They need rest, relaxation,

On reflection I feel that I should be more specific. Your dwarves need many things in order to stay happy and emotionally balanced. They need rest, relaxation, socialization, friendships, relationships, family, music, dance, worship, knowledge, culture, art, beauty, competence, alcohol and nostalgia. (And possibly several others that I have forgotten.) One or two of these things can be gained while they are working, but the rest all require that they not be pursuing tasks dictated by the player, which means that they are counted as “idle”.