Can people lack a comparative advantage and a comparative disadvantage? Source: Question 9b, p 61, Principles of Microeconomics, 7 Ed, 2014, by N Gregory Mankiw
= Question 8b in Principles of Microeconomics, 4 Ed, 2008


  9. Are the following statements true or false? Explain in
  each case.
  b. “Certain very talented people have a comparative
  advantage in everything they do.”
  
  Answer: b. False; it is not true that some people have a comparative advantage in everything they
  do. In fact, no one can have a comparative advantage in everything. Comparative
  advantage reflects the opportunity cost of one good or activity in terms of another. If you
  have a comparative advantage in one thing, you must have a comparative disadvantage
  in the other thing.


Abbreviate comparative advantage as CA. Mankiw's question above motivates the titled one.

E.g., suppose in a 3-person economy: person A's CA is cooking and person B's foraging, yet person C does nothing.
Comparative advantage doesn't work like that.

If person A's CA is cooking, person C has a comparative advantage in foraging. With B, C has a comparative advantage in cooking.

It's not possible to have a comparative advantage or comparative disadvantage in everything: If you were better at everything than someone else, you would have an absolute advantage. As soon as two people have different skills for anything, they have a comparative advantage of some kind.

It is possible for two people to have no comparative advantage/disadvantages whatsoever: If both people are exactly equal at everything they can do, then there is no comparative advantage or disadvantage between them at all.