Answer
Condorcet noticed that majority voting by itself doesn't tell what society truly wants.
Work Step by Step
If society were to use voting between candidates A and B (and the winner would be against candidate C), the public might choose candidate A. If society were to use voting between candidates B and C (and the winner would be against candidate A), the public might choose candidate B. If society were to use voting between candidates A and C (and the winner would be against candidate B), the public might choose candidate C.
Under this situation, each of the three candidates would be chosen. (Usually, one candidate would have a majority and be chosen outright.)
