At a table of new people you can hear yourself editing — the sentence forming, then a second version, then whatever comes out, which is usually the safest of the three.
With two old friends the lag disappears. Same person, same vocabulary, wildly different ease, which suggests ease was never a fixed trait you either have or lack. It runs on how much surveillance you believe you're under, and it loosens as that assumption softens: most people are far too busy managing their own three drafts to be scoring yours.