Childhood experiences contribute to anger set points
Children who grow up in families where parents (or other caregivers) are quick to be provoked to anger are themselves more easily aroused to anger as they grow older. This is especially true for children who are born with a more intensely emotional temperament.
This is one of the reasons for FireWorks. By controlling and properly modulating their anger, parents can decrease both the frequency and the intensity of their children's anger within reasonable ranges set by temperament.
Next: Psychological factors can influence the anger set point