Free Lunch Is Opportunity Cost In Economics - https://en.wikipedia.org/wiki/Opportunity_cost
Just saying: there is such thing as a free lunch, it usually involves a trade off (free lunch at a bar if you order a muinimum of drinks).
TINSTAAFL - There is no such thing as a free lunch.
The above only makes sense in reference to equity speculators who expect no risk. I do not agree that the comment, acronym, or that the phrase replaces opportunity cost in economics. It is also my opinion that the phrase is dated and out of touch with modern economics.