One of the most infamous sayings about advertising is, “Half of my marketing money is wasted. The problem is I don’t know which half.” Somebody should have fired the guy who said that.
The truth is, you need to know which half (or quarter or eighth) is working for you. Another truth: there’s really no reason you can’t know. That’s not to say measuring results is easy, but it is a must. Read on, and you’ll forever avoid being one of the non-measuring masses.