I've been playing this game for only about 6 months. First post here.
I was getting a bit bored with the usual rock crafts based economy in my forts, so I thought I'd switch things up and try out the textile industry. Everything was going smoothly (other than my supplies of rock nuts disappearing for no discernible reason) until the third spring when I had my first siege. Since my military wasn't very well equipped just yet (I had just finished construction of my magma forges), I quickly made a burrow consisting of the entire fort interior to get my citizens behind the surface walls and then raised my drawbridge. Shortly thereafter, I saw dwarves cancelling drink orders due to having no water sources, and realized that while I had been preoccupied with the deep forges, I had emptied my wood stockpile. My brewer had been slacking off for at least a couple months since he had no barrels to fill, and since there were a dozen goblin archers outside my walls, chopping new trees wasn't an option.
But, I knew how to deal with moments like this and had already picked out a good spot for a well on my hospital floor. The well would draw from a reservoir that I would dig out next to a cavern lake which could be safely sealed off by a floodgate. The construction would probably take about 3 minutes.
...Except as my miner begins to channel out the well, he just stops digging. Stuck in the bottom of a 6 z-level pit he just dug, he decides to stop. "No job" it says.
The floodgate and mechanisms are ready, more and more dwarves are complaining of thirst, and I'm wondering what kind of lazy my dehydrated miner must be to choose this moment to lay down on the job. I have my other miners begin to dig another path to finish the well, ruining some of the aesthetics of my fortress layout in the process, but they too get about 90% to where they need to be, and then stop.
At this point I'm cursing loudly at the miners while the first dehydration death occurs, I immediately bring up dwarf therapist and make EVERYBODY a miner. I skip the well entirely and simply designate the removal of a 3-tile thick wall on the cavern z-level so the population has access to the subterranean lake. The workers arrive and dig out one.. two tiles.. and then STOP. A 1-tile thick wall separates my thirsty fortress from an infinite supply of fresh water, and nobody seems to want to touch it. Then the waves of dehydration deaths begin.
It is precisely at this moment that I realize: the citizens are still restricted to the burrow I just made. The burrow which so happens to end exactly one tile away from the lake...
And... FACEPALM.
Of course, a quarter of the population is already dead by the time I am able to fix this error. The tantrum spiral begins just as a mood fails. In the chaos, someone flips the lever in the legendary dining hall which lowers the drawbridge. A dozen elite goblin archers immediately charge my entrance. Their rain of arrows make remarkably short work of my 30+ war dogs...
The population of my fort was 100+ before the siege began. It is now 17 (including 2 babies). The survivors are teetering on the brink of insanity in clouds of miasma as they try to clean all the blood from the floors and carry the countless bodies (and their many pieces) to the mass grave on the surface.