A catcher and his body are like the outlaw and his horse. He's got to ride that nag till it drops.
Some things you know about, you know what the ingredients are - maybe not all of them. But it's up to you to put in the amount. It's up to the director to nag you until you get it right.
The punters know that the horse named Morality rarely gets past the post, whereas the nag named Self-interest always runs a good race.
I keep going over a sentence. I nag it, gnaw it, pat and flatter it.