In the period in which Euripides' Medea was composed, one of the most important virtues was considered to be self-control or moderation (sophrosune). This was considered a particular virtue of the Spartans, but also one in general possessed by Greeks rather than barbarians and more characteristic of men than women. Moreover, lack of moderation is considered one of the vices to which those with excessive power, such as tyrants were particularly prone. This sentiment is expressed by the nurse who says:
… Ruthless is the temper of royalty: […] How much better to live among equals. […] Let me decline in a safe old age. The very name of the "middle way" (21)
Both Jason in his unmoderate desire for power and Medea in her desire for revenge are examples of lack of sophrosune resulting in disaster.