I'll go first...
1. Not speaking to customers daily.
2. Hiring the wrong people.
3. Prioritising short-term wins over long-term goals.
4. Obsessing over competitors.
5. Relying on ads to acquire users.
What else?
1. Paying engineers to build out revenue infrastructure instead of working on core product.
2. Thinking STRIPE will handle this when you start selling up-market.
This is what I've struggled with in the past — appreciation without conversion.
I don't care how much people like what I'm doing unless they pay for the service. This mindset switch helped me effectively navigate the ship towards success from stormy waters.