We are in control of our behavior
A child often becomes angry toward the frequent and aggressive teasing of his father. The constant ridicule becomes associated with anger.

Now the child grows up. The slightest teasing causes an immediate, strong, hostile emotional reaction in his brain. He no longer has a choice to react differently emotionally. In fact, the thinking part of his brain (the outer part called the cortex) is not even engaged at all. The only part that reacts is the inner, emotional brain called the limbic system (especially a structure called the amygdala).

This does NOT justify a person's behavior. Yes, a behavior can become a habit (a mother screaming at her children when she's angry, for example). But habits can be changed and new forms of behavior learned. We may not be able to stop ourselves from feeling angry in some circumstances. Even so, we can establish control of what we actually do.