Even a healthy cat can go through an occasional bout of being a finicky eating. The conventional wisdom is that you should "wait it out and he'll eat when he's hungry enough." But what these laypeople don't realize is that if a cat fails to eat (or under-eats) for long enough, they are at risk of Fatty Liver Disease. This is basically a feedback loop where not eating makes the cat feel sick, and the sicker the cat feels the less they eat, which makes them feel worse. Next step: liver failure.
Then again, you might just want to give your cat a special treat, maybe for her birthday, or for a holiday!
Either way, there are several great options out there for treating a happy cat, or coaxing an unhappy one to eat.