20+ year old reader I guess as an engineer, building the product itself seems to be the easy part. How do you market it, find potential customers, or indeed KN

20+ year old reader I guess as an engineer, building the product itself seems to be the easy part. How do you market it, find potential customers, or indeed KNOW at all that your product is a winning one? Obviously uncertainty is a part of every entrepreneur, but I would love to get opinions from fellow engineers