If you had a gold mine would you teach others where is it?
So why all those people are pretending to be able teaching you something?
Why they are just not making money themselves with all that wisdom they have?
It is interesting that you bring this up, it is widely know that many of the books which contain trading systems are created by people that do not trade and that earn their money by selling books about how to trade, if you took the time to backtest their systems you will realize that they lose money on the long term, but those people know that people will not take the time to verify who they are or to tests their systems so they can get away with their scam and no one exposes them for what they are.
And what is wrong in teaching someone from your friends your own profitable trading strategy?