Why most debriefs produce nothing
The standard debrief is 'so, what did everyone think?' asked of twenty people at the end of a long day while the taxis are arriving. The two most confident people say it was great, everyone agrees, and the session evaporates.
A debrief has one job: to connect what just happened to how the team actually works. That connection does not happen by itself, and it does not happen if the questions are about feelings alone.
A structure that works
What happened? Facts first, before interpretation. 'Our team spent nine minutes planning before we built anything.' Getting the group to agree on what occurred is surprisingly difficult and worth the time.
What did you notice? Observations about the group, not conclusions. 'Nobody asked the other team for help even though we could have.' Still no analysis.
So what? Now interpretation. What does that pattern mean? Is it a pattern you recognise?
Where else? The question that does the work: where does this show up in our real work? If nobody can answer that, either the activity was wrong or you are asking too early.
Now what? One concrete thing, with a name and a date. Not 'we should communicate more'. Something like 'we will put a named owner on every handover for the next month'.
Facilitator habits that decide whether it works
Ask the question and then stop talking. The first answer arrives after an uncomfortable pause roughly every time.
Do not answer your own question, even when the answer is obvious and the silence is long. A debrief where the facilitator supplies the insight teaches the group that insights are the facilitator's job.
Take the uncomfortable observation seriously rather than smoothing it. If someone says the activity was pointless, ask what would have made it useful. That exchange is worth more than four positive comments and the room knows it.
Write the 'now what' down where everyone can see it, and send it out the same day. An action nobody can find by Thursday did not happen.
How long, and when
Fifteen minutes for a short activity, thirty for a half-day, forty-five for a full day. Shorter than that and you are collecting opinions rather than drawing conclusions.
Debrief immediately. The quality of recall drops sharply overnight, and a debrief scheduled for the following week will be cancelled.
One exception: for emotionally heavy activities, a short debrief on the day and a second, optional conversation a week later catches things people were not ready to say in the room.