Cassius's ability to persuade other people to do what he wants can be considered a sign of strength or weakness. He does not possess the inner strength of the other three principal characters, Caesar, Brutus, and Antony. These men are all admired and respected, but Cassius is not. He knows that by himself he cannot organize a conspiracy againist Caesar but that if he can get Brutus to act as the leader, others will readily join in. This is not only because Brutus is so highly regarded, but also because Brutus is Caesar's best friend. If Brutus is turning against Caesar, then there must be good reason for an assassination. The fact that it takes so many men to bring Caesar down shows how strong a man he is and how much they fear him.
Shakespeare inserted a few lines of dialogue in Act 1, Scene 2 in order to demonstrate the kinds of reactions Cassius has been getting from nobles he has tried to sound out about killing Caesar.
Will you sup with me to-night, Casca?
No, I am promised forth.
Will you dine with me to-morrow?
Ay, if I be alive and your mind hold and your dinner
worth the eating.
Good: I will expect you.
Do so. Farewell, both.
Cassius is, above all else, a greedy, selfish miser. He invites Casca to supper because that is a light evening meal and it will cost him little for entertainment. Casca's rude responses are not signs of a surly character but are intended to show that he doesn't like Cassius, that he really doesn't want to join him for a meal, and that he knows what kind of food to expect. Cassius will bring out his cheapest wine and serve miserly portions of food.
Caesar says to Antony:
Yon Cassius hath a lean and hungry look.
Misers are characteristically lean- and hungry-looking. This is because they don't even like to spend money on themselves. No doubt Cassius's entire staff of servants is also lean- and hungry-looking.
Cassius ups the ante, so to speak, when he asks, "Will you dine with me tomorrow?" Now he is offering Casca a full dinner. Casca still would prefer not to come because he obviously doesn't like Cassius and doesn't care if he knows it. But Casca realizes that Cassius will keep inviting him for tomorrow, the day after, and so on, until he runs out of excuses. It is especially noteworthy that Cassius says, ". . . and your dinner worth the eating." Casca has known Cassius all his life and therefore knows what sort of dinner to expect.
Shakespeare shows Cassius's mean nature throughout the play. His selfish character must be well known to everyone. That is why he realizes he cannot organize a conspiracy alone. That is why he has had to develop cunning and craftiness, a craftiness that Brutus would consider unworthy of himself. Caesar says of Cassius:
Yet if my name were liable to fear,
I do not know the man I should avoid
So soon as that spare Cassius. He reads much;
He is a great observer and he looks
Quite through the deeds of men: he loves no plays,
As thou dost, Antony; he hears no music;
Seldom he smiles, and smiles in such a sort
As if he mock'd himself and scorn'd his spirit
That could be moved to smile at any thing.
Cassius has learned how to manipulate men by studying their characters and then appealing to their dominant personal interests. His own interests are always in his security, profit, and advancement.