For some, Brutus is the play's protagonist, despite the fact that Julius Caesar is the play's title character. Why? Well, because the play revolves around Brutus's actions and thoughts. We can always trust Brutus to have honest intentions, guided by his love of Rome, even if this means turning against his friends. Brutus, like any protagonist, has a flaw: he's too trusting and can't tell a mean hand when he's been dealt it. Brutus can see some troubles, like when Cassius accepts a bribe or Caesar aspires to tyranny, because those actions are pretty clearly problematic. It's the more subtle stuff that's lost on Brutus: for instance, he can't see below the surface of Antony's pledged loyalty, which is really planned treachery. Brutus wouldn't betray the trust of an honorable man (and he knows himself to be one), and he assumes, fatally, that he can hold Antony to the same standard.