Success
What are the criteria for success?
If you do not know what success looks like before the day, you will not recognize it when it happens.
Success criteria are what you and the organizer agree would make this workshop worth the time it cost. They are not the agenda or the activities; they are the outcomes those activities are supposed to produce. A session might succeed because the group made a decision, or because a team that had been stuck got unstuck, or because twenty people left with the same understanding they did not share when they arrived. The form of success depends entirely on the purpose.
Criteria that are specific are useful before the workshop as well as after. If you know you are trying to leave the day with a prioritized list of three options, you can design backward from that output. If you know success means a group that feels heard and aligned rather than a deliverable, that shapes the design differently. Vague criteria ('a productive session') cannot guide design decisions.
It is also worth having the success conversation with the organizer and with participants separately, because they sometimes mean different things. The organizer may count the day a success if a decision was reached; participants may count it a success if they were genuinely listened to. Both matter, and knowing both in advance prevents the day from serving one at the expense of the other.