Why is it important to build a brand instead of selling a single product? If you have one product on Amazon then you’re going to be very vulnerable. Anything could happen that could affect your product. For instance, an increase in competition in the market or a change in something from the supplier, this could affect your business then you might lose it.
So in order to be successful, build a brand then launch products within that brand.  However, before you can do that, you need to create a strategy first. Get familiar with your product and your market. You have to send a clear message to your audience.