Brutus, a man of high social standing and good reputation in Rome, is self-conscious about his position. While he never really comes across as arrogant, like Caesar often does, he too has a considerable measure of pride. We see evidence of this in his early conversation with Cassius, when the seeds of the conspiracy are sown. Cassius has been arguing for Caesar's removal; Brutus has been listening, and promises to think about it. Then, significantly, he adds:
Brutus had rather be a villager
Than to repute himself a son of Rome
Under these hard conditions as this time
Is like to lay upon us. (I.ii.172-175)
We immediately note that Brutus is speaking of himself in the third person here, in a very grand manner (something that Caesar also does). This shows Brutus's sense of self-pride and self-worth. He would rather be the lowest of the low in society, he says, a mere 'villager' rather than a prominent Roman, if he is not able to prevent Rome from falling under the sway of one man (Caesar). This is exactly the frame of mind that the manipulative Cassius wants him to be in.
Brutus's pride stems in no small part from his sense of family honour. In a later scene he remembers his illustrious ancestors who expelled the early kings of Rome, thereby helping to establish the Roman republic:
Shall Rome stand under one man's awe? What, Rome?
My ancestors did from the streets of Rome
The Tarquin drive, when he was call'd a king.(II.i.52-54)
Brutus feels he must emulate his renowned ancestors and put all other considerations aside for the good of Rome; he feels he has to act to stop the possibility of Caesar establishing a dictatorship and thereby ending the republic. This leads to his tragic inner conflict; he is moved to murder Caesar, a personal friend, because he feels it is his duty to do so.