Certain parts of his soliloquy of Act II, Scene 1, are important in that they demonstrate how Brutus is tragically flawed.  

• First of all, Brutus reaches his decisions, not through logical reasoning, but in terms of his emotions.  As he ponders whether Caesar will be just if made emperor, Brutus worries that Caesar, if given too much power, may become too distanced from the people, and be heartless in the exercise of his authority:

The abuse of greatness is when it disjoins
Remorse from power, and, to speak truth of Caesar,
I have not known when his affections sway'd(20)
More than his reason. (ll. 18-21)

• Secondly, his conclusions are not logically deduced, but, rather the results of assumption. For instance, from his concern that Caesar may become cruel and heartless, Brutus assumes that power corrupts:

 
But when he once attains the upmost round,
He then unto the ladder turns his back,
Looks in the clouds, scorning the base degrees
By which he did ascend. So Caesar may; (ll.21-27)

        Further, Brutus also assumes that Caesar will be like"the egg of the serpent" and develop into a tyrant. So, in his fear of tyranny, Brutus, feels he should be prevented from this possibility. 

• Thirdly, Brutus is too idealistic in his decisions, failing to consider the possible ramifications of them.  For, as he ends his soliloquy with the decidion to kill the "serpent's egg," he does not consider what social disruptions the death of the popular Caesar can effect.