Person A has something you want. You do something. Person A gives you the thing you want. You win, because now you have the thing you want instead of Person A.

Person A has the authority to license use of something you want. You do something you do not want (tell an untruth, say "thanks" after being slapped, that sort of thing), but that Person A wants. Person A gives you said license, this time. The next time, you'll have to do the trick again, or no license. Instead of getting closer to issuing the license of use yourself, you actually cement yourself into the skinner box.