Before I started a building systems service business, I feared that there would be times when I (later we) couldn't perform the work. That never happened as I recall. All my problems were in getting new clients, more work and running a business what with payrolls, financing, taxes, and dead beat customers. I suppose it's the same in photography. Once you learn the skills to take a decent shot, you have to find customers and run a business. Don't forget to take courses in these disciplines as well.