If you're making your own products you should know everything about what is needed to produce the products, where to source what you need, who makes it, what the markets for your suppliers are like and, of course, everything about the production technology. Whether you're making your own products or not, you should know everything about the products, every characteristic, how the characteristics are defined and measured, how they are improved, why they are important and where the limits are. You also should know how your product is normally shipped, how it can be shipped and how much it costs to ship different ways. You should know about its packaging and how much insurance costs. You should be certain that you will not have any surprises.
Most small businesses have their focus on their products and their business.
It should be on their market. You should know who is going to buy your products and how much the products are worth to them. You should know what your customers value about your products, what they dislike and what they don't care about. It's not that hard to find out about your potential market - just ask potential customers before you start. Everyone thinks they are going to do everything better and make more money than the people who are already in the business.