Stress
Once you take this irregular path through life, stress will become your middle name (just like Idina Stress Menzel and Terrance Stress Mann). No matter where you are in your career as a song-and-dance guy or gal, you'll find yourself asking the same tough questions: "Will I book this job?" and, "Will I ever book a job?" and, "Will I ever work again?" The answer is typically the worst response you could find on a Magic Eight Ball—Reply hazy, try again.
This is your life: rejection, unemployment, and uncertainty. Even hardened veterans never completely let go of that fear during auditions of totally missing a note, or flubbing a line, or tripping over their two left feet.
And if you actually book a job? Weeks and weeks of constant rehearsals and training and dress rehearsals and tech rehearsals and eighteen-hour days and gallons of coffee to start every day.
Then there's the added separation from family if you're in a traveling show—or even if they just don't live in New York. Performing musical theater for a living is incredibly stressful—but if it's also your passion, then it's the good kind of stress.
Except for the unemployed-and-hungry part. That's not as good.