When a company goes one way and its competitors go another, it pays to consider what exactly is going on. E-commerce site Etsy (ETSY -2.25%) has seen its shares lose more than a third of their value over the past 12 months, while Amazon and Shopify have gained 66% and 100%, respectively.Etsy's declining stock price has attracted bargain hunters looking to buy the stock on the cheap. But before investors start loading up the stock, they must understand the factors behind its poor performance. Only then can ...