Do you get angry?
Does it just happen to you?
Do you feel you can't help getting angry?
Is anger a choice? Or a result?
From the point of view of consciousness, anger is a choice... yet the choice was made so long ago, that our present day habitual mind has forgotten the original sponsoring thought.
The original thought is still there in our mind, it hasn't dissipated with time and melted away. That sponsoring thought is responsible for the anger that "just appears" in our adult life.
How does this even happen?
This usually begins as a shock to the psyche when we were young and emotionally defenseless.
Unlike the cells of the body which can heal on their own when they're damaged, the psyche has no cell-like things to induce healing of a mental shock.
The shock may be small or large, it doesn't matter to the mind. If there isn't a parent or guardian to soothe us at the time of the shock, to say to us, "it's okay, it's okay," then the shock lingers like a wound in our psyche, and gets irritated when a later situation reminds us of the original wounding.
So we may find that we're grown up and it can still feel like we can get angry "just like that," as if we have no choice in the matter.
It takes a lot of awareness and intention to catch ourselves as we get triggered to not go into any habitual reaction. This is what some forms of meditation can do, but not all. The best meditation can train our awareness to be more aware of what goes on in our mind, and catch it.
"Well, anger is a natural result of injustice," you say.
There may be a time when you may experience injustice "out there" and still not get angry. You may find that entirely possible. You may retain your peace and have unjust situations around you. You may watch the strong emotions ride up, swirl around, and flow past.
And then see if anger is a choice... or a result.