what is the mean of this.gameObject or gameObject.gameObject?
Both GameObject and Component have a gameObject property which returns the GameObject the Component is attached to, or in the case of GameObject, returns itself
gameObject and this.gameObject are the same pretty much, both of them accessing the gameObject property of your script, which is a Component
gameObject.gameObject gets the GameObject as above, but then gets it again from the GameObject - a complete waste of CPU cycles
