A child gets scared just on seeing a doctor because it is related to the doctor giving him an injection needle in his previous time. This is an example of:
Classical conditioning
The child's fear response to the sight of a doctor, formed by pairing a neutral stimulus (doctor) with a painful one (injection), is a textbook case of classical conditioning as described by Pavlov. The child has learnt to associate the doctor with pain even without a needle being present.
"Give me a dozen of healthy children. I can make them doctors, judges, teachers, beggars and even thieves."
"Give me a dozen of healthy children. I can make them doctors, judges, teachers, beggars and even thieves."