As a group, brainstorm possible sources for the undesirable outcome. Collect as many inputs from the team as quickly as you can. Tap sources of data such as documented problems, lessons learned and other documentation from prior projects, checklists, and templates. Use the idea from quality planning of “asking why five times” to probe for causes, not symptoms. Focus on the quantity of ideas, not the quality; you can filter later.
Organize the results into major cause categories such as: