The knowledge possessed by a medical doctor is fine as far as it goes, but is not much good without the ability to draw valid inferences. This is why you need to be involved in your own healthcare and not just do whatever the doctors say. Sometimes they don’t listen to you or hear what you have to say, and other times they draw conclusions that aren’t warranted, or fail to draw ones that are.
It’s a good illustration of why proponents of liberal education say that a non-expert in a particular field can judge the findings of experts if he is educated in the liberal arts, because he is capable of detecting invalid inferences; and also why being educated in a scientific or technical field exclusively is an incomplete education. And why we should not trust experts to rule society merely on the ground of their expertise in a narrow field of knowledge.