why are we so vulnerable to external forces?

Sometimes when I am annoyed or frustrated, I would sit down, quietly, trying to perceive this sense of frustration, or other emotions, gradually building up in my mind. It stirs, ferments, vents all the way through my chest, and eventually fills my entire mind. Unsettling though it is, it is quite singular and bizarre to observe: a way that, despite my constant concentration, couldn't be swayed by my subjective wills at all. At this moment, I would either read a deep novel or do some math problems, anything that would distract me. Yet after I finished, those unnerving sentiments would all just vanish and fade away. What's left is nothing but an enduring awe to the intricate story of the novel or a deep appreciation towards the wonders of the math world. I would be really startled by this. I sincerely know how hard it is to shun those ingrained emotions, and yet this ingrained emotions just pales in comparison to those external activities of our body. How could that be? Are our mind, our emotions, nothing but puppets strung by those external influences?