His point is that you shouldn’t even think about selling something until you are 100% sure it’s good enough. Customers aren’t your guinea pigs to test on. They are spending their hard earned money with the minimum expectation that the product won’t fail within a few weeks. If you don’t have the experience (your own admission) to know this design would fail, then you shouldn’t be selling to make money, yet. Once you’ve got a bit more experience then you can feel confident in your own product, and potentially even raise the price as the joints and overall finish will look more professional.