You hustle? You sit there and think what is the literal next step, then you try that thing, reevaluate, and repeat. Then keep doing it until you're rich, broke, or dead. There is always something you can be doing.
Doing something is a strict superset of doing something valuable, the key is to bring value, which the quoted comment was addressing.
Waiting until the product is 'ready' to get the wheels turning on sales and marketing can lose you valuable early insights and make it take longer to see if your product fits the market.
This 100% true and an almost unavoidable occurrence when non-technical and technical individuals attempt to start something together. I'd say it's extremely important that if a non-technical individual is coming to a technical one to build literally everything they dream up, said non-technical individual absolutely must be doing an equivalent amount of work in other areas of the company. Sending emails and taking calls/meetings only gets you so far and will eventually be perceived as "0-net" tasks by the technical individual if they don't result in anything.