This picture of Chinese traffic jam has become one of my favorites lately:
Unfortunately I think it characterizes the amount of things some people think can be done in parallel. A Product Roadmap that has nine things that should be developed in parallel. By one team. Of about nine persons. If you say it out loud like this, it's probably evident that it's not going to happen. But if you just add boxes to a PowerPoint, it's deceitfully easy to just add one more box. ...and yet one more.
My solution asks for another picture.
"There you go. I think your Roadmap is great, but it only has this one flaw. Everything you have there needs to fit through this funnel." Well the diameter of the funnel of course depends on the team size, but I think one-piece-flow would be something to strive for.
Doing things in priority order one by one. Creating the features that offer the biggest customer impact and added value one after another. Doing things pragmatically and keeping the focus. Let's try to get there!