You have already given the answer of your question. The quote you mentioned from Al Brooke says everything. He said for obtaining a professional degree you have to go college for years. Then in some professions you need to do internship. But when it comes to trading people are not willing to dedicate their time labour. Trading is easy if you are willing to give enough time for learning. How much time it will vary from person to person as everyone's learning capacity is different.
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