I know zilch about biology or medicine but my impression is that in biology even A->B doesn't imply A->B half the time. Like you might do a large study and find

I know zilch about biology or medicine but my impression is that in biology even A->B doesn't imply A->B half the time. Like you might do a large study and find that people get obese after consuming fat, only to later find that if you do the same with a different group of people, that doesn't happen. (Exaggerating with an example here, not actually claiming this particular example is true. Just trying to illustrate my impression of what a lot of things in the field are like.)