Good business advice is to build products and services around things you already know well. Then you can focus on one hard thing at a time; building a great product.
But not all innovators do so with something they already knew. In fact sometimes innovators are successful precisely because they brought fresh insight into an area where the experts already knew everything there was to know.
You can build a product that relies on expertise that you have to learn as you go. This is a lot harder, but possible.
The trick is to truly commit to becoming an expert in the new area; it is difficult to fake it.
You can accelerate the building of expertise by building on things you already know, skills you already have, and bringing in experts to learn from and build immediate credibility.
To really succeed you have to commit to organizational expertise; being (among) the best in your field and having the world know that (or at least the part of the world that matters).
So a great software product requires both software expertise and subject matter expertise.
So you can build something you know or you know about something you build… but knowing and your product go hand in hand.
P.S. Organizational expertise includes everyone, not just developers and business analysts. Sales, marketing, customer support, management….