It is quite astonishing how often events occur either in the general market, or in individual stocks, which exacerbate a trend that already exists. If you already in such a position, then you are able to profit from these unusual price 'shocks'.
The latest such instance has ocurred with US stock Knight Capital, which has been in the news the last few days.
The chart of the stock shows that there was a downtrend already in place, and you could have entered this around the $12 level in mid-June. If you had, and trend followed, then you would have made a tidy profit on this trade.