As a founder and startup mentor I have seen a lot of startups go their first steps. And there is one mistake I see very often.
Founders often think about building and launching their products how they see big companies like Apple do it: They see Apple working for years in secret on the new iPhone and then launch it with a big event and everyone is going crazy, buying the product and making Apple rich.
So they start building their product based on assumptions in their heads what their users may like and finally after a year of building in secret they launch the product and expect that now they are done and can sell that to the masses.
But in most cases these products fails because at least some of their assumptions were wrong and they build the wrong product.
Because what they didn't see in the work of companies like Apple is the excessive user research and testing and continuous improvement based on that feedback that is necessary to build an innovative product.
When you build an innovative product (what most startups are aiming for), you don't have all the information in advance, you need to experiment and find out, what the users actually need and how to serve that need.
The startup accelerator Y-Combinator always says as a founder you should focus on writing code & talking to users.
You build a first product, test it with real users and learn what works, what doesn't work and try to do better with the next iteration of the product. The faster you can go through these iterations, the faster you get to the products your users actually need and that you can scale for the masses. So building the first product shouldn't take years, ideally it should take days or weeks.
This step is very hard for startups in an early stage - especially first time founders. They have very high expectations on their product and think that's what their customer have, too. They think that their customers won't like the product unless it has all the features.
But your early customers don't really care. If they have the problem you are aiming to solve they will gladly use your product if it can make their life easier - even if the whole process isn't as smooth as it could be.
And you learn so much by having real customers use your product and most of the times you see that what you thought your customers would need, isn't what they actually need. So don't waste too much time building it and focus on experimenting and continuously increasing the value for your users who already use the product.