It's real easy to be in this business when everything is going okay. Sex, Money, Golf, Power, Debt the usual. Long-term success in freelancing is fueled by desire, and desire is completely internal. The truth is, a successful freelance career requires long hours, discipline, and focus. Desire is the magic ingredient that allows you to find joy in the process.
Desire is fairly bulletproof except when it comes to long-term stress.
Be careful with this. Stress kills creativity. I have heard it said that if you must continue to be creative during times of high stress, you may as well arm yourself with plenty of tracing paper and a stack of CA magazines because YOU, my friend, are out of the loop, creatively speaking. Desire keeps you focused so that the time you spend working is productive instead of wasted motion. You can eat right, exercise, party, enjoy your hobbies, take vacations, spend time with your family and generally experience the world - which in turn makes you a better designer.