Can have a circle of competence for a particular industry, but not a circle of competence for individual companies within the industry. It easy to say that the manufacturing of PCs will grow enormously over the next decade, but hard to say which company will dominate. We have decentralized Berkshire Hathaway to the point of abdication. The only thing we have centralized is money. Discount future cash flows at the long treasury rate.
Businesses get credit for free cash.
With the best businesses, you don't need to keep putting in cash. Investing is the art of putting in cash now to get more cash later on. To understand a company, understand its products, its competition, and its earning power. The best way to teach finance is to focus on easy cases. For example, in 1904 anyone could see that NCR was a wonderful company.