The tools used by economists to analyze business firms are too abstract and speculative to offer any guidance to entrepreneurs and managers in their constant struggle to bring novel products to consumers at low cost.
Economics as currently presented in textbooks and taught in the classroom does not have much to do with business management, and still less with entrepreneurship.
Roughly speaking, when you are dealing with business firms operating in a competitive system, you can assume that they're going to act rationally. Why? Because someone in a firm who buys things at $10 and sells them for $8.00 isn't going to last very long in that firm.