Final answer:
Debriefing sessions are best conducted by a neutral third-party to ensure objectivity and effectiveness, especially when internal mechanisms fail or are not in place.
Step-by-step explanation:
Debriefing sessions are most effective when facilitated by an independent party who was not involved in the incident response effort. In situations where an informal approach hasn't worked and no internal mechanism is available to resolve issues, it becomes necessary to bring in a neutral third-party. This external facilitator can conduct the debriefing without any preconceived notions or biases, thereby ensuring a more objective and productive session. This is particularly helpful in identifying areas for improvement and in learning from the incident to better prepare for future situations.