Generate a full detail guide on how to conduct a business 'pre-mortem.' The guide should be a step-by-step facilitator's manual. It must include: 1. An explanation of the psychology behind why a pre-mortem is more effective than a standard risk assessment. 2. A detailed agenda for a pre-mortem meeting. 3. A list of prompts to encourage creative and critical thinking from the team. 4. How to categorize the identified risks and create a mitigation plan for the most critical ones. Please include a supportive disclaimer.