Think as a private owner

A common analogy Buffett used was to compare owning a stock to owning a farm. He said: "If you own a farm, you don’t think you need a quote on the farm selling price every day, and you don’t think the farm’s value gets down 80% because a couple of bad years, or the quote is low."

That analogy is the right altitude and first mentioned by Ben Graham. However, this is one big difference between owning a farm and owning a stock. In the first case, as the owner, you have full control on everything about the business. Not only you make full decision on operations and finances, you also hold full knowledge on the business itself. That brings the full confidence to you and makes you focus on earning power of the business rather than the market quotation.

On the other hand, people care the market quotation of stock because they don’t have full control and full knowledge about the company stock. Therefore, their only confidence lies in the ability of selling the stock "today" at the market price.
That doesn’t mean it is the right way to think about stocks. This is just to explain why they would think in that way naturally. The right way is acquire full control or let someone you can fully trust to take full control of the company, and try to acquire as much as information as you can about the company.

That is why good management is very very important.
Thinking as a private business owner, you only need three things to succeed:
1. Good average estimated return on the investment.
2. Control on the business or let someone you can trust to control the business
3. Diversification.