People frequently judge doctors by the progress of the patient following their intervention. If the patient improves the doctor is competent. If the patient does not improve or deteriorates the doctor is incompetent.
Many illnesses especially acute ones like viral infections are self limiting and not affected significantly by treatment. The condition starts and gradually worsens over days until it reaches a climax, then it starts to improve until it recovers. If the patient sees a doctor in the beginning of the illness he is likely to deteriorate in the following days irrespective of what the doctor does. The doctor may be blamed for the deterioration. If he then sees another doctor when he is at the climax of his illness he will start improving irrespective of what the doctor does. The improvement may then be attributed to the second doctor. The same thing applies to many chronic illnesses because they have a fluctuant course with spontaneous exacerbations and remissions. Justice is rare in this world. It is a sad fact of life.