ὃ γὰρ βούλεται, τοῦθ' ἕκαστος καὶ οἴεται → what he wishes to be true, each person also believes to be true | what he wishes, each person also believes
ὑπελθεῖν: απαρ. αορ. βʹ του ὑπέρχομαι.
