Well, medical students are taught "When you hear hoofbeats think horses, not zebras", meaning to look for the most obvious and common reason for a person's symptoms.
Such if a person presents with fatigue they check the person's iron levels, white cell count etc - looking for that horse - the common cause for the person's symptoms.
However when no common reason can be found, often frustratingly years later, medical professionals start to look at the rarer possibilities behind a person's symptoms.
It can be a very lonely, frustrating and difficult journey with many let downs and in one cases being misdiagnosed until you finally get the right diagnosis.
But like zebra's, rare illnesses do exist.
|"We are a rainbow of possibilities"|
So those with rare and conditions, like myself, we are referred to as 'Medical Zebra's'.