The brief is never the brief
Every commission arrives with a stated goal and an unstated one. Learning to hear the second is most of the job.
A brief tells you what a client wants to publish. It rarely tells you what they want to be true afterwards, and those are different problems.
The stated goal is usually a deliverable: eight hundred words on a product launch, a founder profile, a landing page that converts. The unstated one is almost always about standing — how they want to be seen by a competitor, a board, a customer who left. If you write to the first and miss the second, you will get notes you cannot act on, because the notes are about the second and phrased as though they are about the first.
Ask what changed
The most useful question I know is not "what do you want this to say" but "why now". Something prompted the commission. A rival shipped first. A round closed. Someone in a meeting said the company sounded tired. That answer reshapes the piece more than any style guide.
Write the version they cannot ask for
Clients are rarely able to articulate the piece they actually want, because if they could they would have written it. Part of what you are paid for is a first draft that is braver than the brief, attached to a short note explaining what you did and why. The worst outcome is that they ask for the safe version — which you can always produce, and which will be better for having been argued with.