"You bought me a present? Why would you do such a thing? I know you think you're being generous, but the foundation of gift giving is reciprocity. You haven't given me a gift, you've given me an obligation. The essence of the custom is that I now have to go out and purchase for you a gift of commensurate value and representing the same perceived level of friendship as that represented by the gift you've given me. Ah, it's no wonder suicide rates skyrocket this time of year. Oh, I brought this on myself by being such an endearing and important part of your life..."
- Sheldon, Big Bang Theory