Everybody has a bad day at work. It's just the people in retail / food service / service industries in general work in front of customers who see it. How many times have we all bitched about our job? And if a customer heard said bitch it would have made us look bad.
I used to work as a bus boy and waiter at Tomato's (no longer in existence) back when I was in HS and College. I had bad days there, but I knew better than to act like I was having a bad day in front of customers. That line of thinking used to be common sense, but it is lost these days. To tie this back to the original topic, I never saw an unhappy Chik Fil A employee. They always have a smile and I am sure some of them are miserable while they are smiling but they push through it.