This is exactly what happened to a forex trader here in the UK a few years ago. If I remember correctly, he deposited £10,000 into a spreadbetting account and managed to turn this initial deposit into something like £260,000.
I don't know how he did it. He must have taken some high risk trades and leveraged himself up to the hilt, but the point is that he never withdrew any of his winnings and you can probably guess what happened next.
His good fortune suddenly came to an end and as his trades started to conspire against him, he lost the plot completely and ended up losing pretty much all of his money.
I feel sorry for the guy but the point is that if he withdrew say £200,000 or even just £100,000 of his winnings, he could have invested it into shares or property and given himself a nice recurring residual income for the rest of his life in the form of dividends and rent respectively. He could also have benefited from any long-term capital growth as well.