Because this is forex. You can make money both ways, if you expect the price to depreciate you sell the currency. If you expect the price to appreciate, you buy the currency. It's not the same as stock.

Now as for the example, you expect the currency to depreciate so you sell the currency. However, midway, the price turned against you and it is now even higher than the price you sell. Thus you are incurring losses. Hope you can understand this newbie explanation from me.