My daughter started arguing right before bed about a Halloween costume. Last week, she overheard me explaining the "I know..." brain-dead technique to a friend. So when she started her second "but...I want" I said, very empathetically, "I know........."
She said "really??" and went upstairs and found another costume. Quick learner.
Good job, mom! Not only was she spreading the word about how powerful "I know..." can be but her daughter heard it and learned it too. Very fun!