You earned that at the cost of the Demand's price confidence. If you hadnt sold that amount.. and probably would have held on to it... There's a chance that the exchange (buyying and selling) would keep on going. Thereby giving you 500K dgb close to your total DGB now (in value).

I would prefer a healthier supply/demand without that sort of speculation

Then again, its always about luck here and there. Ah well,..