The context of the following conversation is Robin went to the restaurant where her friends worked, because she knew they would give her food.:
Robin says I just had the best lunch and it was free!.
The friend responds That's great. How did you get a free lunch?.
Robin responds My friends work at the restaurant and they always give me free food when I stop by..
The friend responds So that means the rest of us are paying for your lunch?.
Robin responds I never looked at it like that before..
The friend responds There is no such thing as a free lunch. Someone has to pay for it..