Glory
You won't experience fabulous success with all of your patients, but when you do—oh my, what a glorious feeling. To experience that one-in-a-hundred breakthrough, when a husband suddenly realizes and accepts that—yes, in fact, he is being suffocating, or when you finally make a troubled teen see the error of his ways and cause him to realize how much pain and emotional distress he's been causing his poor single mother.
The tough thing is that you can't yell "Yippee!" or "I did it!" when the breakthrough happens. It sort of ruins the moment.