Buying stocks in the retail sector can prove tricky. That's because a lot of things can happen quickly, such as changing consumer tastes, a failure of the retailer to adapt, or missteps that prove difficult to overcome.It's important to keep those factors in mind when analyzing companies in the sector. Costco Wholesale (COST 0.28%) and Kohl's (KSS 2.82%) have both been around for a long time, but their results and stock prices have gone in different directions.Can Costco keep the momentum going, or does Koh ...