Answer : Trading is a profession and also a business. Any profession needs proper education & training. And any business needs proper planning, knowledge and experience. Self learning is good. Nobody will forget the lesson when they face lose. But the question is how many lessons a person learn by losing money? Since the risk in trading is more, newbie's get in to the grip of fear and greed.
Self learning takes more time as we have to test everything we learnt by trading. It also cost more as each mistake will be punished by a loss. Nobody will realize the money they loss, but if a person keep track of their loss, then they will know how fast they lose money.
The main problem is newbie's dont know what mistakes they are doing and how to correct it. Guidance from an experienced trader will help to overcome it.