One of the chief functions of a product roadmap (and one of the key skills of a successful product person) is to get everyone excited about the future. A roadmap will paint a picture of a world where your customers are happy and your company is successful, making everyone in the organization want to be a part of it.
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If your why (aka product vision) is compelling, and your how plausible, you’ve got people hooked, and they’ll be happy to discuss how they can add their particular what to the plan. See Chapter 9 of Product Roadmaps Relaunched.