When you don’t say what you’re thinking, for the benefit of the listener.
Real world example:
I sell jewelry at the Renaissance festival. It’s made from Swarovski crystal. Cue Drunk Hippie Chick stumbling up and slurring out,
“My niece has ADD and is a pain in the neck – which crystal should I get to calm her down? What kind of energy do these have?”
My thought: “If I throw one at you it’ll have kinetic energy.”
My words: “I’m sorry, but these are man-made crystal. You may be looking for mineral crystals – go see my friend Tom, ‘round this path, near the elephant rides.”