You train the physical body by doing exercises.  The more you exercise, the stronger grow the muscles until what once was a challenge is now quite easy.  The same is true with your emotional and mental bodies.  You can train yourself to respond from the heart, even when one lashes out.  You can train yourself to trust the spirit rather than the human mind.  And so, exercise these faculties over and over.  They do atrophy, but they never do go away, for they are of your True Self.