Neatly making the acronym TANSTAAFL, the phrase 'there ain't no such thing as a free lunch' simply encapsulates the whole theory of capitalism.
The invention of the phrase is usually accredited to visionary science fiction writer Robert A Heinlein, in his book The Moon Is A Harsh Mistress. In the novel there is a sign over a bar saying 'Free Lunch', but it turns out that this can only be had if you buy drinks at twice the usual price.
Its fictional origins have not prevented this little phrase from being absorbed into mainstream economics. For maximum effect it should be uttered in a sneering tone whilst leaning back on your heels, right thumb hooked into the waistcoat pocket of your hand-tailored Saville Row suit1, left hand holding a glass the size of a football2 containing vintage Armagnac. The more wretched the circumstances of the recipient of this pearl of wisdom, the better.
TAANSTAFL is now thought to be one of the most useful neologisms3 on Earth. And perhaps the most annoying.