Acquiring users is very hard. Making them stay is even harder.
As a small, bootstrapped startup you have to show your value from day 1 and you have to keep proving your worth.
Hiring the right people and building a strong team. It's tough to find folks who are not only skilled but also align with your vision and fit the startup culture. Spent way more time recruiting than I anticipated but it was crucial for successfully launching and growing.
Deciding on what to build next.
I think prioritization of limited resources is the single biggest thing for success and failure in tech products, I have seen.