This started when I found Guillotine available to play free online at http://www.gametableonline.com/. Then I noticed that the game was going a little differently than I expected!
See, Guillotine has three rounds and I always played that when one round (or "Day") ended, the next player continues to start the next day. But that's not actually how the game is played. The player who goes after the player who started the first day starts the second day (and then continuing with the third day). Confused? Here's how it goes: There are twelve nobles in each day. Players A, B, and C are playing. Nobles are collected by players in this order: A, B, C, A, B, C, A, B, C, A, B, C. Now "C" collected the last noble but "A" doesn't go first on the next day - "B" does because "A" started the first day!
WHOA! This COMPLETELY changed my strategy for the game! Because, if I'm player "B" in the above scenario, I KNOW I'm going to start the second day so I want to do everything in my power to end day 1 on my turn. Makes the Scarlet Pimpernel a very useful card indeed!
Likewise, I was misplaying Clerical Error. This card allows you to "collect" a noble from another player's scorepile and then they collect one from yours. What I was missing was the trigger word, "Collect." A lot of nobles have an action that is triggered when they are "collected." So, for example, if you "collect" Robespierre from somebody's scoring pile that action ends the day just like if you collected Robespierre from the noble line.
There were a few other examples of how I THOUGHT I knew the rules but, in fact, I was playing wrong. You can check out the official FAQ for Guillotine at http://www.boardgamegeek.com/thread/217462/offical-guillotine-faq.
I guess it pays to check out erratas, clarifications, rulings, and FAQs when you're playing a game - even a game you think you're very, very familiar with. The shame of it is, for some of the rules, I actually liked the way I was playing better... =)