In the play Julius Caesar, is Cassius an inflexible person? If so how?

Cassius seems like a very motivated and determined person, but he is not inflexible. He frequently displays his flexibility, or adaptability, in the play. For instance, in the big quarrel in Brutus's tent in Act 4, Scene 2, he tries a number of different tactics to get his way. He tries the threat of violence, and when that doesn't work with Brutus he tries offering his dagger for Brutus to kill him. Cassius finally understands that what really concerns Brutus is the way Cassius displayed disdain for their friendship in denying him the gold he requested.

I did send to you
For certain sums of gold, which you denied me,
For I can raise no money by vile means.
By heaven, I had rather coin my heart
And drop my blood for drachmas than to wring
From the hard hands of peasants their vile trash
By any indirection. I did send
To you for gold to pay my legions,
Which you denied me. Was that done like Cassius?
Should I have answer'd Caius Cassius so?
When Marcus Brutus grows so covetous
To lock such rascal counters from his friends,
Be ready, gods, with all your thunderbolts,
Dash him to pieces!

Cassius then stresses friendship for the rest of the conversation in order to win Brutus over.

Brutus hath rived my heart.
A friend should bear his friend's infirmities,
But Brutus makes mine greater than they are.

Cassius loses the quarrel--but there is no further mention of the gold. Cassius evidently keeps it, and that is what is important to him. If Brutus does not have the gold to pay his soldiers, they may not fight very enthusiastically at the battle of Philippi.

Cassius is continually submitted to Brutus's wishes. He does not want to fight Antony and Octavius at the Philippi, but he consents against his will. Earlier he wants Antony to be killed along with Caesar, but Brutus disagrees and Cassius has to give in. Then Cassius is really horrified when Brutus agrees to let Antony speak at Caesar's funeral, but Brutus overrules him again, with disastrous results for both men.

It would seem that Brutus is a more inflexible person than Cassius. Cassius is handicapped because he is cunning and articulate, but he is not liked by the other Romans. He is notorious for having a bad temper and throwing tantrums to get his way. He is a miser. He is selfish. He needs someone like Brutus to act as a figurehead, but then he finds that he can't control him as he thought he could. Since Cassius and Brutus work so closely together, Shakespeare took care to differentiate their personalities. Cassius is petty, Brutus is noble. Cassius is greedy, Brutus is generous. Cassius is cruel, Brutus is always kind. Cassius can be a phony, Brutus is always upright and honest. There are many obvious differences between these two partners.