but that's the unrealistic part. in the real world people don't understand each other all the time, but all those "sorry, what did you say?"s would be annoying

but that's the unrealistic part. in the real world people don't understand each other all the time, but all those "sorry, what did you say?"s would be annoying on screen (like so many other things that are skipped in movies). actors don't talk naturally at all, it just seems to us that way because we're used to them talking like that on screen.