In Shakespeare's Julius Caesar, Caesar himself speaks the lines: “Yond Cassius has a lean and hungry look; / He thinks too much: such men are dangerous.” The lines occur in Act 1, scene 2.

Caesar does not know it, of course, but he is being prophetic here. Cassius is dangerous. He will be the one who leads the conspiracy against Caesar. In fact, not long before Caesar says these words, a Soothsayer has warned him “Beware the ides of March.” Caesar does not take him seriously, calling him “a dreamer.” Yet the Soothsayer proves to be right, and perhaps something deep inside of Caesar grasps that.

After the Soothsayer's prediction, Caesar exits for a time. He is in the midst of a victory parade. Cassius and Brutus stay behind to talk, and Brutus expresses his fear that the people will make Caesar a king. Brutus loves Caesar, but he has his doubts about any person having too much power. Cassius has major issues with this, too, and he does not wish to kneel to a person he considers his equal or even his inferior. Caesar is simply too feeble to be a king. Cassius' pride is wounded by the thought of Caesar holding so much power, and we can see the wheels turning in his mind.

Caesar can see this on some level as well, and he notes that Cassius “thinks too much.” That is, indeed, what Cassius has just been doing. Cassius is also “lean and hungry,” perhaps hungry for power in his own right and certainly lean and meager in compassion and loyalty. Antony tries to reassure Caesar that there is nothing to fear from Cassius, but Antony is wrong. There is plenty to fear from Cassius.