This is the dumbest thing David DeAngelo ever came up with, but bless the man for thinking so hard to come up with metaphors like this.
SUPPOSE that you were a busy man with an interesting life who got laid a lot and had a bunch of woman pursuing him. Just SUPPOSE that for a moment.
Now imagine that you're a girl interacting with such a man. Sometimes he'd be unavailable, sometimes he would be preoccupied, sometimes he would treat you to his presence.
It would SEEM like he was "pushing" and "pulling" you.
It's really a gigantic statement about your social value and self-worth. If you're just plain old available all the time, you can't be worth very much.
So David DeAngelo teaches this so that people can try to SIMULATE high social value, but in fact it's a lot less complicated to just HAVE high social value to begin with.
The pushing and pulling will then happen automatically. (Although come to think of it, I still do keep a mental tab in my head... a score of sorts for anyone I interact with... to make sure I'm not being too available or too unavailable... one day, I'll probably even stop doing that... it already happens mostly automatically)