You are wrong on your assumption. Trader needs to find strategy and trading instrument that fits trader's personality.
mate start with small consistent money and slowly build but from the tone of your post that isnt your style. Your attitude is similar to most of the 90% who flunk out of this business.
One should definitely know more than one market, but to trade more then one is only possible if the trades are either automated or held for long time. High frequency intra day trading can only be done on one market. But once this one market is mastered, it is all pretty much the same with some nuances.