Zebras? What the-?

There is a saying in medicine: "When you hear hoofbeats, think horses, not zebras."
That is to say, if a patient comes in with a cough they probably have a cold. Not cancer, not bird flu, not an alien ready to hatch in their throat.
But no one goes into medicine for the horses.
No one would enjoy House if he diagnosed his patients with colds and sent them on their way.
We want to hunt the zebra, gosh-darnit!

Zebras are the things that make life exciting. They're the things you didn't notice at first glance. The things that were always lurking under the surface, waiting to be discovered.
A zebra is the new girl at school with the potential to be an everlasting friend.
Zebra hunting is switching majors five times and then finding your future in an extra curricular activity.
You catch a zebra when you don't get into the school you want, just to get into a better one.

We're trained not to expect the zebras.
But they are out there.