It's hard to explain the concept of overdiagnosis to the public. Think of overdiagnosis as "pseudo-disease," in which something innocuous is labelled as a disease, and leads the patient down a pathway of unnecessary testing and treatment. An example would be finding and treating a prostate cancer in a 75-year-old man who would never die of the cancer. After treatment, he may end up incontinent, or impotent, or have chronic bloody diarrhea.
We know this happens in groups of people. But we can't tell which individuals this is happening to in real time. When we find a prostate nodule and it turns out to be cancer and we treat it, it is really a correct diagnosis. But it's also true that only a few of these lesions will progress to dangerous disease, and we can't absolutely tell which ones ahead of time. So if we do this to ten people, and only help one, we have correctly treated the one but harmed the other nine. Meanwhile, all ten will say, "I beat cancer!"
Harm looks like benefit.
Let's assume that the 9:1 ratio is correct (it's not - I just made that up - I'm totally oversimplifying and I'm not a urologist). Then you're the guy on the exam table deciding if you want to find out if there's a nodule in your prostate. Let's lay it out for you, in this imaginary scenario:
"OK, if there's a nodule there, and it's cancer, there's a 90% chance that if we treat you, it will have been for nothing. And there's a 10% chance that you will get another five years from the treatment." Would you always choose to go ahead? What about if you were 85 years old and had severe emphysema? That's the kind of decision-making we have to encourage in medicine - because it describes the real situation. And, I think, it's the right way to get informed consent.
There's a great textbook that helps docs outline these options.