Generally yes, for a reasonably healthy person and a typical flu for example, that's all anyone would need. The exception is if there's any complications because of the infection and that's just playing the odds. In those cases there are anti-viral drugs and other treatments but they usually come with a long list of side effects. It's usually best to let the body fight the infection itself and just support it. That said, every year tons of healthy people are disabled or die because of very common illnesses so it's not so black and white. Generally speaking, you are correct, but don't let that stop you from seeking care if you think you need it.