The Ultimate Peter Principle?

What happens when someone's promoted beyond his or her skills? We learn something about this from the fate of Caius Marcius (sometimes Gaius, sometimes Martius), later Caius Marcius Coriolanus.

Marcius, one of Rome's greatest generals, is successful in war: eminently successful in Rome. He is so successful in war that he's nominated for Consul. Marcius protests that he has not the skill nor the temperament to be Consul. Various of his friends, allies, and family—especially is power-hungry mother, Volumina—persist.

Marcius fails to tame his temper and his tongue, and is banished from Rome. He allies himself with one of Rome's enemies and, eventually, is murdered by those enemies.

Is Marcius's death because of his changing allegiances? his eventual susceptibility to his mother's entreaties? to his inability to acquire the new skills needed as a politician? to his pride?

As an aside, Volumina reminds me of Julia, Caligula's grandmother.