Challenge provides a systematic pre-mortem plan analysis framework to help an agent find weaknesses in any plan before reality does. By imagining the plan failed 12 months from now and working backwards, it surfaces core assumptions, maps vulnerabilities across confidence and impact dimensions, and establishes dependency chains. It includes specific challenge patterns for product roadmaps, go-to-market plans, hiring plans, and fundraising plans. Use it before committing significant resources, presenting to a board, or when feedback has been one-sidedly positive.