I understand, but the question is "who leads the individual Roman Catholic and Orthodox to believe that the teaching of their church is right?"
The answer to who leads the Church
From The Catechism
813 The Church is one because of her source: “the highest exemplar and source of this mystery is the unity, in the Trinity of Persons, of one God, the Father and the Son in the Holy Spirit.”259 The Church is one because of her founder: for “the Word made flesh, the prince of peace, reconciled all men to God by the cross, . . . restoring the unity of all in one people and one body.”260 The Church is one because of her “soul”: “It is the Holy Spirit, dwelling in those who believe and pervading and ruling over the entire Church, who brings about that wonderful communion of the faithful and joins them together so intimately in Christ that he is the principle of the Church’s unity.”261 Unity is of the essence of the Church:
All individual Catholic’s are to follow or they are not in unity