PH Community: Biggest challenges/surprises you faced when building a community around a new product?

Talking to all marketers here but also everyone else that might have some experience with community building. What has been your experience with community building and what were the key challenges you faced and maybe surprises along the way that you didn't expect when planning. When launching a new product it's all about getting people to use it, to buy it and build off of their feedback, so having a community is crucial for success. In some nieches it's easier to launch a new product and get a community of customers and users around it, sometimes it's harder. Sometimes you can use existing communities around your business or brand to kick start the community around the new product. Also the choice of social platforms is always crucial. For some products your community will be on Instagram, for others it might be LinkedIn. Have you ever been surprised by finding people and a community for your product in a place you didn't think of or expected? One of my biggest challenges is handling the expectations. Building sustainable communities is such a tough and long-term process, but nowadays I often come across unrealistic expectations in terms of community size and the time to get there. Do you experience the same and how do you handle it?