Quality
can lead to sales - this was the premise behind the original Google (they never spent a dime on advertising their own product until the Parisian Love commercial [1] came out in 2009, a decade after founding), and a few other tech-heavy startups like Netscape or Stripe. Microsoft certainly didn't spend a billion $ marketing Altair Basic.
The key point to understand is the only effort that matters is that which makes the sale. Business is a series of transactions, and each individual transaction is binary: it either happens or it doesn't. Sometimes, you can make the sale by having a product which is so much better than alternatives that it's a complete no-brainer to use it, and then makes people so excited that they tell all their friends. Sometimes you make the sale by reaching out seven times to a prospect that's initially cold but warms up in the face of your persistence. Sometimes, you make the sale by associating your product with other experiences that your customers want to have, like showing a pretty woman drinking your beer on a beach. Sometimes, you make the sale by offering your product 80% off to people who will switch from competitors and then jacking up the price once they've become dependent on it.
You should know which category your product fits into, and how and why customers will buy it, because that's the only way you can make smart decisions about how to allocate your resources. Investing in engineering quality is pointless if there is no headroom to deliver experiences that will make a customer say "Wow, I need to have that." But if you are sitting on one of those gold mines, capitalizing on it effectively is orders of magnitude more efficient than trying to market a product that doesn't really work.
[1] https://www.youtube.com/watch?v=nnsSUqgkDwU