Brutus has a tendency to ignore his fears and insecurities without dealing with them, like the person who wobbles on his bike. He says that "between the acting of a dreadful thing/ And the first motion, all the interim is/ Like a phantasma, or a hideous dream" (II,i,63). Even as he steps into the role of one of the leaders of the conspiracy, he still has doubts about their cause. In II, i, 163-183, Brutus makes fine distinctions to justify killing Caesar in order to banish his own insecurities, not simply to maintain the nobility of the conspirators' cause. However, he suppresses his own fears about the rightness of killing Caesar and goes through with it, insecure till the end.
Though Brutus suppresses his fears about the rightness of killing Caesar, they come back to haunt him literally in the form of Caesar's ghost. The ghost is a manifestation of Brutus' doubts, identifying himself to the Roman as "thy evil spirit Brutus" (IV, iii, 281). This encounter, which Brutus sees as a supernatural visitation of doom, convinces him that he will die. He takes this revelation relatively calmly, as the fitting punishment for a murder that he never felt good about in the first place. We see the ghost not as a real supernatural spirit, but as Brutus' inner fear. When the ghost disappears, Brutus says, "Now that I have taken heart thou vanishest" (IV, iii, 286). When his fear vanishes, so does the ghost.
Not only does he attempt to hide his misgivings from himself, Brutus hides fears from others. He tells Cassius, "before the eyes of both out armies here,/ which should perceive nothing but love from us,/ let us not wrangle" (IV, ii, 43). No matter what private grievances and doubts their leaders may have, the army must remain confident and believe that all is well. Brutus knows from personal experience that working for a cause while not being completely convinced of its rightness just makes the situation more difficult.
One plus for Brutus is his ability to listen to other people's rational fears and not their overemotional manipulations. Cassius persuades Brutus to join the conspiracy by playing on realistic fears of what Caesar might become in I, ii. However, Cassius' threat to stab himself relatively unaffects Brutus during their argument in IV, iii, 106-112. He recognizes Cassius' temperamental, overdramatic state and doesn't take him too seriously. On the other hand, Brutus does not see other potential risks, such as leaving Antony alone with the crowd to manipulate them against the conspirators (III, ii, 62). He places too much trust into Antony's intentions.
Though Brutus might have had the potential to be a great leader with his true desire to serve the people, he has fears and doubts about the rightness of his cause. These insecurities, along with a lack of suspicion in regards to Antony, lead to his downfall. Brutus kills himself partly to atone for the great crime he feels he has committed in killing Caesar against the will of the people.
While playing Brutus, an actor should constantly emphasize his insecurity and fear that he was not doing the right thing. He shouldn't seem too confident, rather more nervous and fidgety. During the scene when the conspirators kill Caesar, Brutus' hand should shake while stabbing his once-friend. After committing the act, he should look in horror at what he had done. Until the end, Brutus should be uncertain and guilty over taking part in Caesar's murder.
Other Characters
Cassius
Julius Caesar
Mark Antony
