I made an account so I could answer. I'm new-ish to DF (I know about it for years, but started to play a few months ago). I find some part of the stress frustrating, either because it's rather ridiculous (Urist is depressed on account of thinking about that time he was rained upon, 10years ago. Urist is now berserk), or because the dwarf are just dumb (Urist is mad because he is away from family. Urist is also a new migrant who decided to come without his family). But that's not the topic if I understand correctly, so I'll point the biggest issue I had concerning morale.
My issue is related to fort defense. I had a wonderful place, with mist generators, temple and all. It conern my military, who had had a barrack with statues, a personal mist generator and so on. Living like kings, really, it was engraved and all. Soldiers where in full steel gear, superior and above, trained for years, and had a few fights with nothing bad to record. Moral was mostly higher than average.
Siege comes. Lots of goblin (a lot). I send my company of dwarven space marines, veteran of several fights, to meet them. And here come the issue.
One of my soldier suddenly (and by suddenly I mean instantly) goes from "I like my life" to depressed. Apparently, my dwarves killed a bunch of gob in a row, and each death inflicted some morale damage to this character. The log had a "death is around us..." about 10times in a row. Note that I pick my military to avoid all the negative traits like "hate war" and stuff. So he wasn't especially prone to morale shock. Also, it was his 3rd or 4th siege, it wasn't the first body he saw.
Fight ended, and my dwarf, now tantruming, went to the tavern (next to the barrack), grabbed a poor peasant and reverted the relative position of his skull and brain. Traumatizing a lot of dwarves forever (tavern was packed).
It was extremely frustrating. That guy was not only highly experienced, but it was not his first fight. And he proceeded to traumatize half the fort.
I want to add that was not a singular case. Fort defence is highly traumatic, to the point I entirely rely on traps nowadays. Between going outside in the sun, under the rain, seeing bodies and whatnot, warrior goes from "I'm fine" to "I want to die" in a single siege. After the incident I mentioned, the next siege had another dwarf lose his mind the same way, and the next. Ironically, I didn't have any dwarf lost in several sieges from fighting, but I lost an average of 1dwarf per siege through mental breakdown and personality shift. Also, I even had my champion lose his mind at some point. A guy who was with the fortress for a long time, legendary in everything, killed a metric ton of enemies, and even had a nickname. He was happy and all, but in a singular fight, his mind broke.
I abandoned the fortress, and created a new one in the same world/same civ. One of those traumatized warrior came in a migrant wave. She had her personality shifted to prone to depression or something, and was a wreck in a permanent state of tantruming. No matter how well she was, a few bad event would throw her from average to depression. Not only I had to deal with that sh** in my previous fortress, but they came to haunt me in the new one. Dwarven stubbornness is real.