Ever hear of Pavlov?
He was a Russian Physiologist who did a lot of experiments that ultimately were able to identify classical conditioning. His most famous involved a dog, dinner, and a bell. Whenever Pavlov would feed his dogs, he would also ring a bell. The dog's natural response was to salivate. Soon, the dog would learn to associate the bell with food so that whenever Pavlov would ring the bell, the dog would start to salivate even if there wasn't any food present. This is the conditioned response and it's a type of learning we are all susceptible to.