Hopefully, most of those that I know are smart and intelligent, too. That is not the complete answer, though. because most of them are logical. There is little logic in short term trading. Long term, perhaps. Short term trading is reflexive and instintive, regardless of what is taught about various signals. In fact, I believe that intraday trading cannot be taught. One either gets it, or he does not.
What is taught is knowledge and experience that the teacher has although, often, he does not have it. He just knows how to pick brains, write and sell a book. That is no guarantee that the student is going to understand what the tutor does. That is why so many systems end in disappointment.