These standards of care do exist for a lot of things. (see NCCN treatment guidelines for ones related to oncology). Oftentimes a doctor will not be reimbursed by insurance if they give treatments that are outside of approved standards. There is leeway given, though, because its just damn hard in many cases. Patients can present with 4/7 key symptoms and may report other unrelated issues. Or ailments can act differently in different people. Or maybe you have never been able to sleep well and don't even notice that, and it's a key issue related for a diagnosis.
1 really interesting point about it, though: They vary WILDLY by nation. You wouldn't think it would make a difference, but because of the varied regulatory bodies, and even culture, it does. (This was an issue that Watson for Oncology ran into after being trained by US doctors. In Japan, even on the occasion is gave a reasonable answer - it was watson after all - it often was not how the Japanese doctors would act in that circumstance).
1 really interesting point about it, though: They vary WILDLY by nation. You wouldn't think it would make a difference, but because of the varied regulatory bodies, and even culture, it does. (This was an issue that Watson for Oncology ran into after being trained by US doctors. In Japan, even on the occasion is gave a reasonable answer - it was watson after all - it often was not how the Japanese doctors would act in that circumstance).