On Persistence

So the guy calls 911. Fire department arrives, with truck and four firemen.
Guy: "He's been walking with little shuffling steps and has lost the ability to speak clearly. I think he has had a stroke."
Fireman 1: "I just did a stroke test, and I don't think he has had a stroke."
Fireman 2: "Yeah, I did the test, too. He hasn't had a stroke."
Soon the ambulance arrives, with two paramedics.
Guy, to paramedics: "I think he's had a stroke."
Fireman 2, to paramedics: "We did the stroke test and he passed."
Paramedic 1: "Yeah, I did the test and he passed, too."
Guy, at hospital, to doctor: "I think he's had a stroke."
Doctor: "I don't think he's had a stroke. His behavior is just the result of his illness. CAT scan shows no bleeding."
Next day.
Doctor: "We did an MRI and it shoes  he's had a stroke."

An Analogy
Guy: "Look at that duck over there. I say 'duck' because it has webbed feet and waddles like a duck."
Observer 1: "It hasn't quacked like a duck, so I don't think it's a duck."
Observer 2: " Yeah, it hasn't quacked, so I don't think it's a duck, either. I think it's a chicken."
More observers arrive. Guy to new observers: "Look at that duck over there."
Observer 2 to Observers 3 and 4: "We don't think it's a duck. It doesn't quack like a duck."
Observers 3 and 4: "Yeah, I've looked at it and haven't  heard it quack either."
Guy, at the veterinarian's office, to the vet: "Can you take care of the duck?"
Vet: "I don't think it's a duck."
Guy: "But it has webbed feet and waddles like a duck and has a bill like a duck."
Vet: "Strange deformities for a chicken, huh?"
Next day.
Vet: "The animal jumped into the pond and started quacking as it paddled around. It's  a duck."

Sometimes you need to get more than a second opinion. Sometimes you need a third or fourth opinion, especially if you have good reason to believe that the conclusions of others are just not right, because they are based on partial, incorrect, or distorted information. Quick, pigeonhole diagnoses should always be viewed with caution.