> If you can be sure you are profitable in say a month (or a year), you are multiplying money, so using leverage or loans you should be able to basically have any amount of money you want (and what about trades in that case?).

Its not that simple, sadly.

You can't buy $InfinteMoney$ worth of stock X in a single transaction, you end up moving the stock price as you buy/sell. This allows others to respond to your activity. At small scales, a system that appears to work will break down at large scales.