But we can usually objectively tell what is wrong. A test can be administered by different doctors and they're almost certainly going to arrive at the same conclusion. Mental illness has so much overlap and comorbidity that we can't really do that. Even for something like ADHD we don't really have an objective test for.
We can tell folks what is wrong if you have a common and fairly well understood disease that has indicators that we can test for. People sometimes wait years to be diagnosed with an autoimmune disorder, though, and these have medicines that can significantly improve life. We find cancer, but sometimes treat everything as aggressive (though it is starting to change). And so on.
Heck, we are still slowly discovering body parts.
The brain is one of those things we still don't know a lot about despite the seemingly broad knowledge we have. Some of the knowledge we have is fairly recent and can be thanked, in part, to modern scanning. I don't know how we can expect folks to have a definite test for this when there is so much we don't know.
