"Vyapara' means activity. Activity done by a living being is called 'Vyapara'. Here occasionally 'Vyapar mean trade or business.
There are two states, conditions of every person. (1) A person cannot become an expert in every act or trade and (2) every person is expert in some activity or trade. This "Nyaya' being on the realistic social background, advises that a person must join, get involved in his own activity or trade but must not join or get involved in an activity or trade that is not his own. To emphasise this concept, to fix up this concept in the mind of a human being this 'Nyaya' came into existence.
E.g. (1) One person is expert in an act of sawing. So it is said that sawing wood is his business. (2) But this man is not expert in cooking. So cooking is not his business. This 'Nyaya' advises such a person must get involved in his own business of sawing wood but must not get involved in the business of cooking.
This kind of Nyaya' is necessary because the person whose business is sawing wood has very clear understanding about what care he should take when he joins his business and does not become a victim of any disaster. But cooking is not his business. So when such a person gets involved in an activity of cooking he (for want of knowledge) may harm himself. Thus, this 'Nyaya' explains that one must not get involved in an activity, business which is not his.
(Note: The moral of the story 'Kilotpati' in Panchtantra is like this only)