On my current fortress i made a terrible mistake.
Originally, my underground farm was rather small, but it was enough for most time.
Unfortunately with the drinking issues (that most likely is a bug) that made the dwarves totally ignoring the water source of a river i designed (adding even part of groud as it was suggested), and even made them ignoring the well i built near the fortress, i had to produce massively alcohol to prevent them running to the other end of the same exact river, in which they could be easily killed one by one by goblins ambushes.
Additionally, with the rabbit level of reproduction of my dwarves, after slaughternig most of my current animals dwarves were needing food a very lot more, i was left finally with too few plants for the size of my population.
So i decided to add a second farm room.
As the ground was not good for farming, i opened with a lever the door to the underground part of the river, getting the ground wet enough for growing plants.
To avoid a stupid dwarf going to his death in water, i blocked the entrance.
Once the ground was wet enough, i closed the river door and dug several room under my farms , dug a staircase, so the water could be drained.
So far so good, but ... i totally forgot to made the entrance door passable again... during a whole season, as i was busy making some walls and channel and bridge outside to improve my surface defense and build some nice paved roads inside my walls.
After a while, all i could notice was dwarves and their kids starving in each corner of my fortress without understanding why.
Then i finally remembered ... the farm door !!
I lost because of starving lots of dwarves and kids and lot of furnitures due to tantrum thrown, but the worse part was the mayor that suddenly went berzerk.
The problem is that the mayor after all those years was a very strong dwarf, he went straight to the bedroom complex that house each dwarf individual sleeping bed, and killed at least 2 dwarves and a kid , along with an unfortunate pet donkey, before my wrestling squad finally manage to come and the wrestler high master broke the berzerker mayor in two.
Since that it took a season to stabilize the dwarves mood, as the farm took lot of time to begin to produce enough to feed them, so i lost some more of the population.
But finally all seems good now.
That's exactly when a baron, his wife, a tax collector and a hammerer decided to pay a visit and begin to ask for more crazy things to be build.
I begin to believe the tantrum spiral will then soon start again.
The new mayor elected to replace the crazy berzerk dead one seems to be a really cold hearted mother , she lost a kid, observed his body decay, lost friends
.... but she is happy