Well, when you do something I ask you too, I tell you you're a good girl. You pleased me, and I am enjoying what you are doing. It's called being submissive, putting my needs even before your own. Dedicating yourself, your body, and your time to making sure I'm happy. In return, I make sure you're happy. And in some cases, like yours, hearing that praise, makes you feel good, so you'll do things to hear it again.