Acharya Prashant explains that mental tendencies or 'vrittis' are responsible for creating the initial, subtle waves of emotion or thought in the mind. While one has no control over the emergence of these initial waves, they lack significant power until they manifest physically in the body. He suggests that since the source of these tendencies is often hidden in the subconscious, one should focus on controlling the physical symptoms, such as the breath. By regulating the breath during moments of anger or passion, the conscious mind is prevented from fueling the emotion further with logic and memories, effectively containing the 'fire' before it spreads.