Linear roadmaps are misleading without a crystal ball for seeing the future. A roadmap that recognizes the existence of risk as time goes on is more honest. But an effective PM needs to anticipate possible branches, too - and create clear criteria for following each path.
ALT Three roadmaps:
Misleading roadmap (linear) - “We will follow this linear path from zero to our inevitable victory, and these are the milestones that will get us there.”
Honest roadmap (conical) - “We know where we are today, and have a good idea about the near future, but recognize that the future becomes uncertain.”
Strategic roadmap (diverging paths) - “We know where we are today, and anticipate decision points that will change our path. We are intentionally gathering the data that will help us make those decisions.”