Within the context of coalition behaviour, proving sources of rationality is one of the main problems in explaining the foundations of cooperative games. Coalitions appear because winnings are super-additive. However, people with rational behaviour choose strategies with under-additive winnings, because winnings and monitoring costs increase with the number of members in the coalition. We need to understand how coalitions are formed. The Jury theorem could be a solution to enable us to understand how groups are formed. Nevertheless, within this theorem two of his arguments are paradoxal.This paper aims to research the compatibility between the Jury theorem and Condorcet's paradox in order to understand how coalitions are formed in the Games theory.