# Help understanding the parkour tutorial in Cocos2d

I was practicing the parkour tutorial for chapter 7, but I failed to understand why we should move the same delta movement of this.gameLayer, which contains the background layer and the animation layer in opposite direction. Why do we do this?

The player is moving (right) relative to this.gamelayer. If this.gamelayer is shifted to the left the same amount, the two movements will 'cancel' each other out.