What does it take to gain more superior knowledge about businesses. Liberal reading about different types of businesses and understanding the finer nuances of them by deeply analyzing the company annual reports. It helps immensely to understand how innovators, entrepreneurs and business execs think, execute business operations. 

Am pasting just 3 paragraphs from Amazon annual report and see how much we can learn about the types of costs or even about the management focus on lowering product costs for customers which has remained the key competitive advantage for Amazon till date.

Below is the excerpt from Amazon Annual Report:

Our primary source of revenue is the sale of a wide range of products and services to customers. The products offered on our consumer-facing websites primarily include merchandise and content we have purchased for resale from vendors and those offered by third-party sellers, and we also manufacture and sell electronic devices. Generally, we recognize gross revenue from items we sell from our inventory as product sales and recognize our net share of revenue of items sold by third-party sellers as service sales. We also offer other services such as compute, storage, and database offerings, fulfillment, publishing, certain digital content subscriptions, advertising, and co-branded credit cards.
Our financial focus is on long-term, sustainable growth in free cash flows1. Free cash flows are driven primarily by increasing operating income and efficiently managing working capital2 and cash capital expenditures, including our decision to purchase or lease property and equipment. Increases in operating income primarily result from increases in sales of products and services and efficiently managing our operating costs, partially offset by investments we make in longer-term strategic initiatives. To increase sales of products and services, we focus on improving all aspects of the customer experience, including lowering prices, improving availability, offering faster delivery and performance times, increasing selection, increasing product categories and service offerings, expanding product information, improving ease of use, improving reliability, and earning customer trust.
We seek to reduce our variable costs per unit and work to leverage our fixed costs. Our variable costs include product and content costs, payment processing and related transaction costs, picking, packaging, and preparing orders for shipment, transportation, customer service support, costs necessary to run AWS, and a portion of our marketing costs. Our fixed costs include the costs necessary to build and run our technology infrastructure; to build, enhance, and add features to our websites and web services, our electronic devices, and digital offerings; and to build and optimize our fulfillment centers. Variable costs generally change directly with sales volume, while fixed costs generally are dependent on the timing of capacity needs, geographic expansion, category expansion, and other factors. To decrease our variable costs on a per unit basis and enable us to lower prices for customers, we seek to increase our direct sourcing, increase discounts from suppliers, and reduce defects in our processes. To minimize growth in fixed costs, we seek to improve process efficiencies and maintain a lean culture.