I would echo Samnotsamuel's comment. High returns such as 200% can only be achieved by taking huge amounts of risk (i.e. very concentrated portfolios and/or using leverage via margin or options)
Let's say you have a few good years and start investing larger amounts of money. Do you really want to risk those hard won gains as much? Probably not.....plus it gets more difficult to buy and sell your positions when you want and in the size you want as your portfolio gets bigger.
Try this: if you have access to a financial calculator that can compute future values based upon certain assumptions, try plugging in different rates of return and the number of years and see what you get.
EX:
PV: $10,000 (present value)
N: 5 years
I: 200%/yr
PMT: none (no additional payments or outflows)
FV: $2,430,000
That might seem achievable, but I guarantee you that the 200% return in year 5 is MUCH more difficult to achieve than in year 1..........