I'm very late but I had some things to add that I didn't feel were mentioned.
Looking here on the wiki we can see the complete list of emotions generated and their effect on stress
https://dwarffortresswiki.org/index.php/DF2014:EmotionIf the game is going to colour code them the thing that makes most sense is to colour code by strength of effect on stress. If there's a pattern at the moment I can't see it.
Knowing what affects stress is one of the ways experts (who know this page on the wiki) can keep things under control.
Second, the stress system just keeps linearly adding up forever. At the end of the second year anyone with less than 0 stress is going to be fine (if you keep them out of the rain etc.) but anyone above 0 is dead.
They are doomed. There is no hope for them. At some point they will go mad and it's just a question of how long it takes for the maths to hit 10000 and how many others they take with them.
I would expect dwarves to reach some kind of stress equilibrium, where more stress has less effect and vice versa for happiness. This can't happen with the current system and is why the anxiety and dealing with stress personality entries are so important, and why the personality change from them is so devastating.
Personally I think the mood change from the rain thoughts is actually ok, it's the mathematically certain madness that results from these depressive personalities that breaks it.
There are two ways a dwarf mitigates stress when it gets bad, shouting at a mayor, tantrums. Any other mitigation can happen at any time and is under player control.
So if a dwarf is stressed they will take these activities to cheer up, but none of them have a strong enough affect to actually help anything. I've never seen them do a thing.
Worse they just mean the dwarf spends forever running to the mayor and never takes care of their other needs.
So there's an attempt at auto balancing stress when the dwarf is very stressed but it doesn't seem to be doing nearly enough to offset the linear steady decrease over time when the daily / weekly adjustment is unbalanced.
I'm suggesting something like, at 5000 stress more stress counts for half and stress reduction count normal. There will be some number here that balances stressed dwarves into a kind of annoying limbo where they can tantrum a bit, shout at the mayor, stumble obliviously now and then, but not be literally doomed. There's still a game in there, not certain fortress destruction.
Finally, I hope the original post by ThreeToe isn't actually what we want...
It's hard to know how bad it is to lose 3 haulers to madness from a goblin clean up because I don't know how many there are or how long after the cleanup he waited but with 200 haul jobs in a death zone and 50 dwarves doing it I would expect to see 10 dwarves go mad over a few years.
In practice you don't let your "real" dwarves haul to keep them away from the death zones. And also you have to keep the haul path for the corpses completely separate to the main fort so they don't see them. At the moment the personality change consequences of seeing a corpse are too risky to let a legendary anywhere near them.
This makes using warriors quite risky.
The way the really bad personalities have such a strong effect has been mentioned by others but I wanted to repeat it. It outweighs everything.
The way friendship/marriage is broken is only so important for stress because of the strength of these bad personality changes and how children is the best (repeatable!) way to get a positive personality change.
The second god not being worshipped only becomes important because of these super sad dwarves who can't be allowed a single unhappy thought.
For what it's worth I managed stress ok in my last fort six months ago, I lost a few soldiers after a fight and a couple of very depressed ones due to personality changes.
I stopped playing because I couldn't make more children without too much bedroom micro, but the stress management wasn't fun either.
