I agree with such point of view like not every human can be a trader, however I think that the phrase should sound like "not every human can be a successful trader". Traders may be unsuccessful. They just can start trading activity, to trade for a little bit and then lose all their money. Such a person is a trader too, but unsuccessful. So, I guess that if a person wants to be a trader then he must own such qualities as patience, calmness, calculating, judicious and dilligence. These are the main traits of a person who can potentially become a succesfful trader.