Well, obviously, you might say: to get well - see a doctor. But I mean it in the sense that no matter how long you (or your child) have been sick, no matter how obvious and revolting the pus, rash, laboured breathing, rapid heartrate, whatever - the moment you sit in front of the doctor all symptoms disappear. What rash? Um, see this kind of faint pink dot here? A moment ago that was a pox covering my whole body. My child who is currently jumping up and down on the examination table looks quite well to you? But I promise he has been bed ridden with a hacking cough for a week!
This rule also works with getting plumbers to come and look at your faulty dishwasher (nope, looks like it working just fine to me ...) and techies to check your computer which miraculously works the moment they come to look over your shoulder.
I'm not sure what the lesson is from this. If you don't go to the doctor, you will stay sick; if you do go you have the expense and embarrassment but walk out cured.