Say you owned a small retail shop (some of you may already do that!). You wouldn't dare think of doing business without asking your customers how they found your store, what they are looking for, or why they were there, would you? No, you wouldn't. But many companies do this exact thing with their online stores.
The easiest way to track what your customers want is to watch what they do online. But since you can't look over every customer's shoulder as they use your website, the next best thing is to watch them virtually through web analytics.