I believe that the "doesn't care about anything anymore" trait makes dwarves move more slowly and drink more.
I was referring to "Used to tragedy" or "Becoming accustomed to tragedy" or whatever they are called.
These are the same thing. "Used to tragedy" is first, and "doesn't really care about anything anymore" is the final stage. It seems to accrue whenever the dwarf loses happiness in small amounts, but gets major boosts when they witness death or suffer injury.
It does not make them any slower or any weaker. It makes them more resistant to mood swings in both directions. They naturally maintain a state of "fine" and sleeping in the dirt or drinking water will barely change their mood. Similarly, fine dining and grand bedrooms hardly give them benefits. At least for short-term. After a long enough time, they reach the full mood swing that the thoughts allow, but have a "lower acceleration" for how quickly their happiness changes.
They also seem insanity resistant or immune. I had one older fort, the lead soldier was danger room trained and candy clad, fought solo against elf sieges and won. He was fully hardened by the time a tantrum spiral arrived, and every single dwarf and child eventually died. He rested at 0 happiness for several months and tantrumed rarely, but never went insane.
Finally, fantastic read, though as above, is this real?