One of my producers said this business is like a hamster on that little wheel thing that goes around and around. You may have a great day and get great ratings, but then you've got another show to do - whatever moment of success or happiness you have you've got to keep grinding it out for the next day.

This quote is talking about how working in the television or film business can be challenging and tiring. It is comparing it to a hamster on a wheel, where no matter how hard or successful the hamster runs, it still has to continue running and grind it out for the next day. It means that although people in the business can have moments of success and happiness, they always have to keep working and going towards the next task and project in order to keep the business running.