Comment by gsmaverick

They are not necessarily related. Information symmetry just means that both parties know exactly the same information and neither knows more or less than the other. In a scenario where one or both parties have information that is not accessible to the other they can still engage in a trade in which each party, at least believes, it is better off given their information. A neutral/third-party observer may not come to the same conclusion but that is not relevant to this scenario.