Step 1: Develop product
Step 2: Market product
But both need to be done in tandem with each other. While you are developing your product you should also be working on some way to either build an email list, establish rapport, get on people's radar, or at the very least validate a product fit and a basic marketing strategy.
For instance if you plan on advertising on Adwords you should be running tests to a dummy page (or email opt-in) before your product launches so that you know if that is a remotely viable option before sinking tons of priceless developer hours into a product with no proven way to market it.
Alternatively if you are going to advertise on forums you better spend a lot of time on those forums to make sure you are creating something those people care about and that those forums have enough visitors to move the needle.
Those are two examples - there are a million ways to market a product and all of the promising ideas should be experimented on and validated before your product is even finished.
Far too often solo cofounders are driven by a cool idea and then handwave (or worse look down on) the marketing aspect of it, and then after their product is finished they are left wondering why they spent huge amounts of time creating a product that nobody is signing up for. When I launched there was no uncertainty - I had already talked to tons of people in the industry, had lots of beta testers, and had properly validated the promotional channels I thought fit best with the product.
But if the creation of a small, passionate audience happens naturally during the creation of any sufficiently good product, is it that much of an obstacle?
And if a solo developer is trying to look for prospective customers, the customer should feel exited about just hearing the product. Otherwise there is no point in pursuing the idea. So there should be no worry about the customer not being interested.
But the parent did say:
> Every one man success story on HN was largely possible due to existing audience from another entity that took years to grow
And I think your experience (and mine) echoes that: the audience didn't happen to be "yours" but it did exist. The problem you have to solve in our case is how to turn a "colder" audience into a warmer one (as it would be if you "owned" the audience already).
How I did it was very simple. I found where my customers were and I lived and breathed on the industry forums they were on. While developing my beta I had a very strong sense of the problems people were facing, how my product solved those problems, and why my product would be superior to competitors. Plus I was able to establish myself as a reputable person within those circles of people on those forums.
So when my beta was ready I was able to get people to pay for the beta by offering them a lifetime discount and the ability to talk with me throughout the development process so that they had some impact in shaping the product. Just from those beta users I was ramen profitable and I was able to bring on an intern for a couple months to help me speed up some of the development.
By the time I publicly launched I had a core group of evangelists (the beta users), a strong reputation on industry forums, and an amazing product that solved big issues my customers faced and I reached 5 figure MRR within a month of launching.