Speaking on the spot is a skill you can practise, not a gift you are born with.
Most of the talking we do is unplanned: a question in a meeting, a word at a leaving party, a reply to a hard email out loud. Abrahams builds the whole book on the idea that this kind of speaking can be trained like any other skill. His six steps are meant to be rehearsed in calm moments so they hold up in tense ones.