Question: what does the phrase theres no such thing as free lunch mean in economic terms
[{'answer': 'opportunity cost', 'provenance': [{'wikipedia_id': '144704', 'title': "There ain't no such thing as a free lunch", 'start_paragraph_id': 2, 'start_character': 324, 'end_paragraph_id': 2, 'end_character': 340, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '144704', 'title': "There ain't no such thing as a free lunch", 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 410, 'bleu_score': 0.8788736777139601, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1858642103374998791}, 'section': 'Section::::Abstract.'}]}]