In the immortal words of our favorite crab, "WoW is a game about upgrading your stuff." While achievements and professions allow for your character to grow, they don't make you any stronger. If you want to increase your power, you need to upgrade your stuff. Gear improvements are often the difference between success and failure on cutting-edge encounters, when your raid needs to meet specific raw damage and healing numbers to pull off a win.
While it sounds easy, it's not always as simple as it seems to upgrade your stuff. While the advent of the ilvl system allows for us to quickly judge the rough quality of an item, it doesn't provide any help when comparing two items from the same dungeon. It also doesn't assist us in our gemming or reforging choices. Making intelligent gear decisions is a part of every rogue's life. In order to make the best choices for our characters, we use what's known as theorycrafting to evaluate the various stats in the game. The end result allows us to make educated gearing strategies and ensure we're doing the most DPS we possibly can. But how do we get from evaluating stats to choosing an actual piece of gear?