For the LotRO Yule event, come quests lock each other out until you complete the other. In one case, this is a bit of logic: you cannot both donate to the beggars and shoo them away. In another, it is a great design choice: you cannot have both the eating contest and cleaning the tables from the eating contest. If you did, you would have quest objectives from both on the same tables, and actually winning the eating contest would be far more difficult as you tried to click the right thing. The design keeps you from accidentally making yourself fail quests.