Bhagavad Gita, Chapter 3, Verse 37

The Deity said: It is desire, it is anger, born of passion; ravenous and full of sin. Know this to be the enemy here in this world.

Unchecked craving is the root, and the moment it's blocked it turns into anger.

Krishna finally names the force behind Arjuna's question. Desire that isn't examined doesn't sit there quietly, it curdles into anger the instant something gets in its way, and that combination is described as destructive.