Wondering how you could possibly fight with yourself?
Your mind is a battleground between two competing parts of your psyche. One center is your conscious Logical-self what we call the Head, and the other is the unconscious Emotional-self or Heart. In Psychology, they call these centers of willpower System 1 and System 2. Your every action rises out of a tug of war between System 1 and System 2. Whether it is something simple like watching TV or something serious like deciding which career to follow, your heart and head rarely think alike.
When your head and heart are seriously out of sync, you can experience everything from stress and lethargy to major mental health problems like depression and acute anxiety. When your Emotional-self and Logical-self are of one mind, you can work as hard as can be and experience nothing but happiness. The ongoing tug of war in your mind...