In this case, it was actually the ABSENCE of a rule - empty spots in buildings aren't filled in with gray citizens unless an event causes them to be placed (or when you place them during setup)! I had assumed all dice should be in the game and, therefore, all the spots should be filled in the buildings when 'Assembling the Workforce'. DRAT! I HATE getting rules wrong.... :( It really bothers me, even if I know it might not have impacted the game much. I know some people might write these off as unintentional 'variants' (ok, sometimes you do this and end up with a better way to play, or at least a different interesting way to play) but it just irks me to get it wrong from the original rules. The absence of the rule along with an assumption is what trapped me here.
So, it got me thinking about some of the traps that Game Explainers might fall into.
Here are some common traps that I have (or seen others) fallen into:
TRAP: Forgetting to teach important rules.
Danger of the trap: Well, this one is fairly obvious - if you forget a rule you can completely change the game, perhaps even breaking it. Also, when you remember it later and let everyone know, they can think you were holding it back on purpose until the moment you 'remember' it and it's to your benefit. Or worse, it can completely ruin someone's strategy and take them out of the game. I have been on the receiving end of this before where I thought one thing and it turned out to not be allowed or something due to a neglected rule.
Example: Caylus - In a 2-player game I played a while ago, the rule not taught to me was where the worker in the Inn can be removed voluntarily the next turn when the Inn is activated or be left there if the other player has not pushed him out. Actually, this doesn't apply just to 2-player. I didn't realize I could remove that worker on subsequent turns - I thought it had to be forced out. I mentioned this and the person I was playing with seemed to confirm it would stay. On the first turn I had placed a worker there and NEVER got him back for the rest of the game as the other player never used the Inn to force me out. So, I was basically 1 guy short the ENTIRE game. The plus side was I never had to pay more than 1 Denier after the other player passed...so at least I had some benefit from it.