What definitely doesn't work when it comes to influencing the roadmap?

Anything has the potential to influence the roadmap, but I’ll answer a slightly different question: What typically doesn’t work when it comes to influencing the roadmap.

Any PM or Product leader who’s worth their salt will use a mix of quantitative and qualitative inputs to understand what they should build next, and so should you. Developing a roadmap, and keeping it updated, is both an art and a science.

So here's what typically doesn’t work: Expressing opinions that aren’t informed by the data or a deep understanding of the market, customer needs, or your competitors. Trying to influence the roadmap in any other way demonstrates a lack of sophistication and erodes a PMM’s credibility. Once eroded, it’s difficult to rebuild that credibility and regain a seat at the table or your PM's respect. That's why it's so important to invest heavily in understanding your market, your customers' needs, and your competitors before having strong opinions about what Product should build next.

(See my other response for recommended approaches on how to influence the roadmap)