Almost the same principle that applies to gambling. People see to forget all the safety measures and warnings way too often. They look to make quick profit or willing to risk large amounts without having the right knowledge.
Greed is something which if not controlled could be dangerous and can have many adverse effects of it. Be it financial, mentally or in relationship it can have the ill effects of it. Also be it trading or gambling, only invest or play with the amount that you can afford to lose as it is not easy to make money from it. Trading require skill and patience to get it right and those who cannot manage it better to stay away from it.