The most important takeaway from my first product is:
«Nobody can build a good product without iterations. Relaunch like a pro. Iterate again and again toward product-market fit. Continue improving on your solution until it actually solves a problem.»
Now, I'm building my current product https://getlanding.io with this mindset.
I have learned to be objective towards my product and my approach to customer acquisition. Most users if not all are not as excited as you are about your product. "wouldn't it be cool..' usually don't resonate with new users unless you are providing the right/most convenient solution to their problems.
My biggest learning was "Do not let the absence of a prototype or beta prevent you from engaging with your target market. Instead, figure out ways to engage your future community on existing platforms — newsletter, social, Product Hunt — before writing the first line of code. Because you'll need those folks to critique what you're building from day one."