Deanna's empathy always mysteriously failed when they needed somebody to get away with lying.
power of convenience. Sort of the same way Data was super fast, but almost never given an opportunity to disarm anyone who pulled a weapon on the crew
My biggest pet peeve about TNG. There's tons of talk about how Data is stronger, faster, and even in Measure of a Man they want to construct more of him to give every Federation ship this advantage.
Yet it's hardly ever seen on screen