I look at it like this. Let's say you, I, and Klutzenhopper are in a square dancing contest. We all do a do-sa-do. Mine is satisfactory. I do what the definition of the move says to do. I get base value.
Klutzenhopper gets his feet tangled up, stumbles and bumps into his partner. The judges decide that he did complete the element, but with errors. He gets base value with minus 2 GOE taken away.
You do a dandy, with great posture and a lively step right on the beat. You show elan, musicality, a feel for the character of the dance, and you throw in a little wink to your corner as you pass by. You get base value plus an extra +2 in GOE for the quality of your element.