It's easier to discuss priorities and roadmap issues one-on-one with the head of sales, for example, than it is if the head of marketing is also in the room. Too many egos, too much politics. I make it a point to continuously "shuttle" between all my stakeholders gathering their input individually, discussing what's important to them, and trying out early versions of the plan on them en route to a final roadmap.
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A little Shuttle Diplomacy goes a long way toward buy in. I go in deep in Chapter 7 of my book Product Roadmaps Relaunched. Got stakeholder stories to tell? Horror stories? Tell me a story.