This is the same reason why a PSP will always give you better fraud protection than rolling your own, they look at so much more data than you ever will that they will be able to better tell friend from foe. Fewer false positives and fewer false negatives. Still too much, but the theory is that in order to be able to detect fraud you will have to have some fraud!
That fails to argue that having any fraud is beneficial; if you have no fraud, there is no value in being able to detect fraud.
That fraud by itself is not beneficial goes without saying.
Just like any classification system a fraud control system has false positives, false negatives, true positives and true negatives. In an ideal version of such a system you have no false positives and false negatives. But that idealized version of that system (the one that perfectly classifies fraudulent transactions and non-fraudulent transactions) is static. It can't adapt to cases of fraud that it hasn't seen yet. Eventually a fraudulent transaction gets through.
And that transaction if not detected timely but after the fact (so now there is some fraud) will result in an update to the fraud detection system (probably it will need more than one example to be able to generalize from). Now the perfect system may start to generate false positives or false negatives on other transactions.
So that's why all of this is relevant. I hope I'm able to explain it clearly enough.