Good point. However, this example could go either way.
Suppose everything you said is true, but in addition to all that, there is a set of symptoms caused by -- making this up -- endocrine disruptors in our drinking water. When pregnant women drink too much, they get some subset of symptoms from a set that overlaps 80% with the cardboard box symptoms.
Now we have two different causes for different symptoms. In addition, you can get the strange case where:
patient A, symptoms X, condition G
patient B, symptoms X, condition H
patient C, symptoms Y, condition G
patient D, symptoms Y, condition H
Although most of the time, condition G will have similar symptoms and condition H will have similar symptoms.
Suppose everything you said is true, but in addition to all that, there is a set of symptoms caused by -- making this up -- endocrine disruptors in our drinking water. When pregnant women drink too much, they get some subset of symptoms from a set that overlaps 80% with the cardboard box symptoms.
Now we have two different causes for different symptoms. In addition, you can get the strange case where:
patient A, symptoms X, condition G
patient B, symptoms X, condition H
patient C, symptoms Y, condition G
patient D, symptoms Y, condition H
Although most of the time, condition G will have similar symptoms and condition H will have similar symptoms.
That's why it is so useful to have a marker.