 Now the real paradox. The tension arises from the dual nature of obligations: they are supposed to be both binding and waivable. Your obligations “bind” you in the sense that you have to comply, other things equal, or else you wrong the person to whom you are obliged. But this person can, if they like, waive the obligation, releasing you from your duty. This duality is perfectly intelligible in the two-person case. If you owe your friend $5 for a fancy coffee, you are bound to pay – you cannot simply opt out, as you might opt out of a mailing list or a volunteer trip. And if your friend wants to unbind you, they can do so unmysteriously, simply by saying “My treat.”