And there are only two things you can do about it.
First, build a solid ground. That would be knowing yourself, your situation, your story, your purpose, your triggers, your strength. A solid ground is what will allow you to not take change personally.
Second, open your arms. That would be listening to others, embracing their fears, helping them with their agendas, navigating the situation together with them, establishing long-term relationships. Open arms is what will allow you to make your solid ground even more solid.
One thing you should never do about change, and that would be trying to control it.
If you are a start-up, with a single product, and you sell to other businesses, then product marketing is basically the foundation of your whole go-to-market.
The way you talk about the product, the way you differentiate from other alternatives, the unique point of view that makes you worth considering, the material you need to go out there and influence people, the knowledge of you target customer and of their pains.
Perhaps you can’t afford a product marketer. But make sure that whoever is doing marketing will focus on those things for at least 80% of their time. It will pay off.