I was still pretty new when I played in
gameID=112282. I was fairly proud of my performance as Italy, which was largely due to my strong Austrian ally. Once we had the game well in hand, I thought we would go for the 17/17 split (again...I was quite new). MarekP, who was Austria, saw my foolish lack of defense against him and took that opening for an easy solo. It's a valuable lesson that I've not forgotten. It also showed me that (occasionally) the Key can work really, really well.
Since then, I've had the pleasure of playing with him several more times...he's an excellent player. What is your best Diplomacy lesson?