In Shakespeare's "The Merchant of Venice," Portia reflects upon the destructive power of jealousy:
How all the other passions fleet to air/As doubtful thoughts, and rash-embraced despair,/And shuddering fear, and green-eyed jealousy!/Be moderate....scant this excess....
and in "Othello" Iago says,
O, beware, my lord of jealousy,/It is the green-eyed monster which doth mock/The meat it feeds on....
Consumed by this "green-eyed monster," Cassius perceives all that is happening in Rome through this "green," unripe and sick vision. Clearly, he is envious of the power that Caesar wields over the Roman people. Even Brutus tells Cassius,
No, Cassius;for the eye sees not itself/But by reflection, by some other things (I,ii,53-54)
Caesar, too, recognizes the danger in the envious Cassius as he remarks,
Young Cassius has a lean and hungry look;/He thinks too much: such men are dangerous. (I,ii,194-195)
These thoughts of Brutus and Caesar prove true when Cassius describes Caesar in this way:
...And this man /Is now become a god, and Cassius is/A wretched creature, and must bend his body/If Caesar carelessly but nod on him.....Why, man, he doth bestride the narrow world/Like a Colossus, and we petty men/Walk under his huge legs and peep about/To find ourselves dishonorable graves./Men at some time are masters of their fates:/The fault, dear Brutus, is not in our stars,/But in ourselves, that we are underlings....Why should that name be sounded more than yours? (I,ii,115-143)
Cassius expresses his envy of Caesar's position as well as his puzzlement that a man of weak physical condition--"the fit was on him...he did shake...His coward lips" (I,ii,120-123)--should be elevated when he and Brutus are his equal, if not superior. It is only that they have not seized power as Caesar has that makes them inferior, he tells Brutus.
While Cassius is consummed with envy, he is yet an accurate judge of character as evidenced by his ability to "seduce" Brutus into participating in the assination plot. Later, when they battle the forces of the triumvirate, Cassius's judgments are the wiser, but mistakenly he defers several times to Brutus and they meet their tragic ends. Certainly, Cassius commits the "tragic mistake" of the Aristotlian tragic hero.