Can I prove it in my own life? Yes. Have I talked to others who have seen the proof in their life, yes. Do I have the research papers to support my conclusion, no. But I’m sure there are some out there.
Human beings have the capacity for both good and evil. Those capacities can be strengthened and weakened depending on our personal life experiences and practices.
Might there be some people who cannot choose due to a psychological ailment or disability? Of course.
I myself use to be a class clown, hurting peoples feelings for the sake of mass laughter. Overtime, I learned to be funny without hurting peoples feelings. That was a choice that I made, gradually, based on me being more aware of what was happening.
I think the key is that when we’re paying attention to what is happening below the surface, inside of our own self, we start to notice things. And the more we notice, the more we’re able to decide what actions we’d prefer to take and which we’d like to avoid.
It’s not going to be perfect, like flipping a switch, but it does start with making a choice or maybe realizing that a choice exists. Then from there we can put the conditions (therapy, meditations, spiritual practice, etc.) in place we need to help us change.