The vast majority of medical malpractice falls under the category of diagnostic error. For example, a really important diagnosis was missed, or diagnosed as something much less harmful.
When doctors evaluate a patient, they come up with a list of potential diagnoses, called a differential diagnosis.
This list usually includes the most common/likely or benign explanations for the patient's symptoms or signs, but it must also include the must-not-miss diagnoses that are dangerous and could kill the patient if not acted on quickly.
Too often, providers either fail to give due consideration to those must-not-miss diagnoses, or give only cursory consideration and rely on unreliable methods of reassuring themselves that the patient doesn't have that diagnosis.
I often see in medical records that the, "patient looked well-appearing."
Since when could we rule in or rule out the must-not-miss diagnoses based on appearances alone?
So many clinicians have been led astray because they did not probe further as required by the standard of care, and instead they settled on a diagnosis that was benign or more likely and failed to work up and rule out the dangerous diagnoses that lurk beneath the surface.
Doctors sometimes use subjective phrases like "non-toxic appearing" or are inappropriately swayed by the subjective pronouncements of patients. A patient who comes to the emergency room with shortness of breath and says it feels like an asthma attack may very well be having an asthma attack. That could be at the top of your "differential" diagnosis, but it is wrong to "anchor" on asthma and not give appropriate consideration to other potential diagnoses.