It is entirely possible to do these manual things, acquiring users one or two at a time, and never having achieved escape velocity where your product does not garner enough attention such that its users recommend the product to others, and it grows by word of mouth itself.

I've built at least two of these that became the most popular solution in their space for a given problem, and if you don't have the constraints of a VC investor wanting their returns and eventually shutting you down, then you can realistically go for years without significant enough growth to even get past par with your direct competitors.

Or you realize that your competitors were never even big enough to meaningfully compete with in the first place because you didn't aim high enough.