What was the biggest learning lesson from your unsuccessful launch?

Last month, I posted about CommonPlace, a new reading app that allows users to store and organize their reading notes while also connecting with other readers. Unfortunately, our post underperformed, and we didn't get as much traction as we had hoped. After some reflection, I realized that one of the main reasons for our lack of success was our lack of focus on community outreach ahead of our launch. Interestingly enough, I learned this mostly through random people DMing me on LinkedIn in the week after our post to support their upcoming launch. This made me realize how important it is to build a community of engaged PH users before launching a new product. What is the biggest lesson people have learned from their launches?