Internal knowledge

Almost any time I talk with someone about the stock market in real life, I'm disappointed about their approach. 

For instance, last week, a colleague told me that almost all his money (retirement money and everything else) was invested in different mining stocks. He also told me that, since inception, he had an annual performance of 5%.

First of all, it means that this guy doesn't read about stock market. Any serious investor has read multiple times that natural resources are not a good way to make money.

Second, if he had read about the stock market, he wouldn't be satisfied with a 5% annual performance. What's the use of investing when you're beaten by the S&P (8-10% every year). 

Third, what about diversification? How could it be a good idea to put all your money in only one sector? And one of the worst sectors possible.

How can you become a good investor if you don't read about investing and thus, learn how to avoid things that make you lose your time and money? It's a big mistake to think that your internal knowledge is sufficient to succed. There's a vast amount of wisdom that's available on the Internet. All your have to do is to triangulate the information by trying to validate and invalidate certains conceptions. 

How can you become a good astronaut if you don't read about space? 

How can you become a good doctor when you can't tell a kidney from a lung? 

How can you become good at anything if you don't put a lot of time and effort in it? It's true for basketball players, musicians, carpenters, lawyers and investors. And for anybody else.