Effective product management requires cross-functional teams because the best products need diverse perspectives to be developed.
It all starts with the PM, but they don’t work alone. They need to interact closely with other company stakeholders from the engineering, sales, marketing, and support departments. Together, they'll develop a product roadmap and development strategy, and assess product-market fit based on what they know about their customers.
For example, after communicating with support teams and conducting extensive customer research, a product manager knows that features A, B, and C are the most important, and developing them should be a priority. This product manager then approaches the head of engineering to explain what needs to be built.
As the engineering team begins to build the new features, the PM starts looking at possible ways to get validation that the team is building the right thing for their users, either through some form of a prototype, a/b test, or a beta release.
Once the product is built, tested, and perfected, the PM typically contacts the CMO at the company and helps to brainstorm product marketing strategies. Bonus points, however, if the marketing team is looped in at an earlier stage: they might add insight and long-term vision to the data points you as a PM have already collected.
As you can see, a successful product team is comprised of multiple company leaders all working toward the same goal: a successful product. But the product manager spearheads their efforts and keeps the entire team focused and on track.