Normally, I am very good whenever a siege shows up, especially when I want to make sure that the enemy runs straight through my trap corridor and gets obliterated by all of my clear glass large serrated disks that also break as they run through them, but they're clear glass, a totally renewable resource from all the wood and sand on my map, so who cares?
I had everything forbidden so nobody would try to fetch Goblin body parts, corpses, or dropped items. I had the traps forbidden so nobody would try to unjam them or pick up any discarded broken pieces and mechanisms when the trap falls apart. I had all the logs on the surface that my dwarves had been quantum stockpiling through the wonders of minecarts and single-tile stockpiles forbidden so nobody would try to grab any and bring them back.
What I did not do was make a burrow that encompassed everywhere "inside" that excluded the outdoors and the trap corridor, and I forgot to disable autochop. So there's my Great glassmaker, who is also a woodcutter, running past my trap corridor and down the tunnel straight into the path of the gobbos on his way to cut down a tree that just grew tall enough to become a tree and become eligible for cutting down, since I have no limits on my stored logs. Every tree must be cut down!
He was just fulfilling his duty necessary to keep those prissy elves we were already at war with since embarkation mad, but he ran straight into the goblins while doing so.
Fortunately, after quickly realizing my mistake and burrowing the entire underground, he managed to survive by turning back, but he did get his stomach cut open and some bones broken, and there's still a silver bolt stuck in his chest, but he didn't lose any limbs and managed to lead the goblins back through the trap corridor where all but one died, and the one spearman that didn't was killed by a swordsdwarf as he tried to retreat.