The Main and Obstacle Characters are counterparts. They represent the two principal sides to the argument of the story. Because they are dealing with the same issues a case can be made that they are not too far apart. This often results in such familiar lines as “We’re both alike,” “We’re just two sides of the same coin,” “I’m your shadow self,” and so on. In contrast, though they are concerned with the same things, they are coming at them from completely opposing views. This leads to common line such as “We’re nothing alike, you and I,” or “We used to be friends until you stepped over the line.”

From the Dramatica Theory Book