Unfortunately, I have learned from experience that it is a great mistake to trust that the doctors know best, regardless how experiences and how expensive they might be.
Regarding treatments, yes, most medical doctors are competent and it is likely that they know better than you.
On the other hand, regarding diagnosis, errors are frequent, for 2 reasons:
1. Most medical doctors are too narrowly specialized and they are experts in their narrow fields but ignorant about other medical domains. Unless you have an obvious problem it is quite likely for you to go to a medical doctor of a wrong specialty and receive a misdiagnosis instead of being redirected to an appropriate specialist.
2. Each human has a complex medical history, which is normally unknown to the doctor who attempts to diagnose you. The doctor might have some past data provided by you or by other doctors who treated you in the past, but that is not enough to know well your characteristics. Because of that, the doctor will try to attribute your symptoms to the most frequent causes encountered at other patients, even if there are reasons in your history that make those causes completely improbable.
I have experienced this several times, when I have received a misdiagnosis and I could not believe it because I know my body and I know how it feels, even if the doctors were right that the symptoms were frequently caused at other people by what they thought to be the correct diagnosis.
Every time, second opinions confirmed that I was right, because even if those doctors had experience with thousands of other patients, I have an experience of half a century with my body and I understand it better than anyone can understand it after 5 minutes of examination.
Regarding cancer, my father broke his arm and he went to an orthopedist, who put a misdiagnosis of osteoporosis.
In fact he had bone cancer. Even if it was a cancer form that has good chances of treatment with some recent drugs, my father lost half of year due to the misdiagnosis and by then it was too late.
I have read a medical manual and my father had obvious symptoms of bone cancer, exactly as they were listed in the manual, word by word (continuous all-day pain, which was confused with arthrosis by the doctor, followed by a bone fracture as a result of small effort, which should not have been enough to fracture the bone, which was confused by the doctor as being caused by osteoporosis).
A competent doctor should have recognized that even if he had assigned the symptoms to what he thought as the most probable causes, there are also other possible causes, e.g. cancer, and he should have sent my father to supplementary investigations, e.g. scintigraphy, which would have discovered immediately the cancer and allowed adequate treatment.
Unfortunately, I was not prescient enough to have read the medical manual before the problem appeared, because I naively trusted that whenever medical problems will appear I will just pay professionals and they will solve the problems.
It did not happen so. My mother also had serious problems because of a misdiagnosis. In her case it was not cancer, but I have also discovered after reading the appropriate textbook that her symptoms were completely typical, but also unknown to the doctor (of a wrong specialty) which consulted her first.
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