It's hard to find customers so it's a good advice to be fully prepared when you're trying to sell a new product. Who'd like to be sold something that's only half working or not fully stable yet?
Reality is somewhat different for new projects. It's preferable to start selling something even if it's not ready rather than wait for the product to be perfect and not find anyone to purchase it.
Close a deal everyday, be it just a meeting opportunity. Even if small, a deal is an open door for bigger deals later on, with the same person or someone else!