Internet advertising is often filled with guesses and assumptions. It can be incredibly difficult to determine whether or not your ads are actually convincing people to buy your product. Some services, like Google AdWords, have conversion-tracking features that can at least shed a bit of light on a customer's path from seeing an ad to making a purchase.
Anybody who's launched a Facebook ad campaign, however, knows how hard it can be to truly determine whether or not those ads are having any real impact. Luckily, Facebook is working on a way to take out some of the guessing.