Brutus brings about his own downfall

When he agrees to Cassius' plot. He's not that kind of man, he's playing along for what he thinks is the better good but when the moment comes to act against Caesar you can see the horror/regret in his eyes. It's terrific acting, top notch.

Brutus has a conscience; he works for what he thinks is best consciously, but his subconscious has other ideas and seems to correct him. It's a much deeper role seeing James Mason playing it than I had imagined reading it, just as how Marlon Brando's Mark Anthony is a much more powerful role than how I read it. It really helps to have great actors performing it to become drawn in and get some emotion from it.