Yesterday I talked about the predicament you’ll be in if you say “what?” to a person just before your brain decodes what they said. Then you do know what they said, but since you said “what?”, you have to be polite and hear them out again. Well guess what? This scenario sets you up for a greater frustration. Fortunately, only a selected few will visit this torture on you.
Some people, when they hear you say “what?”, assume that whatever they said was incapable of conveying their meaning. That is, they figure you heard every word they said, but you failed to comprehend. So when you say “what?”, they repeat themselves in entirely different words, maybe even entirely different meanings. That’s okay if you really didn’t hear them the first time, but if you really DID understand them already, you know they’re now saying something entirely different, but politeness prevents you from acting on this knowledge. The point? Same as before. Don’t say “What?” too soon, give your brain a chance to decode first.