Hall of Doh!

[Sawyer]

This is apparently a fairly common mistake, actually.

My biggest D'oh! was spending the better part of 10 turns acquiring the materials for making some artifact-level gear for Taurotyrannos (the Pangaean blood minotaur hero, I think that's what his name was,)along with a Black Heart to make the most powerful assassin known to half-mankind, sending him into a province and having him seize upon a generic commander...
Only to have him cast tangle vines incessantly because I forgot to script him. And watch him die. And watch the commander get ahold of the Manreaper and all sorts of other nifty stuff.
D'oh!