Dwarves are fickle creatures, and when pressed to the breaking point of their happiness, they will tantrum. A tantruming dwarf may attack people and animals, destroy buildings, or throw things. The dwarf will receive happy thoughts from doing this. Those acts are generally considered a crime.
Dwarves will tantrum if they are at the "very unhappy" level of happiness or worse. If a dwarf has created a masterpiece-level item, they will also throw a tantrum if it rots, or is ever destroyed or stolen. Masterpiece engravings can be destroyed by miners digging out walls or floors.
However, dwarves will not tantrum if a masterwork item is sold to foreigners, or if a masterpiece building is dismantled.
Okay, so I've never had a tantrum spiral happen to me, but from stories I've heard, it seems that one pissed off dwarf can destroy 80% of the population by pissing the rest off. Isn't this a little extreme? I can understand that this isn't a smiles and sunshine game, but it seems a bit unfair to completely cripple a fortress over a masterwork engraving being collapsed.
Do dwarves have a personality trait that dictates how they handle grief? I think it's odd that most dwarves react the same way in a lot of cases. Not every dwarf would run around hitting people if his artifact was destroyed or a loved one died. Some can be unhappy in peace, thus stifling the tantrum spiral.
Someone tell me if I don't know what I'm talking about, but I think that dwarves should have more unique chances to tantrum, and more unique behavior during a tantrum.