When students first learn about Pavlov's dogs--that dogs learn to salivate to the sound of a bell (the "conditioned stimulus") when the bell had been sounded before the presentation of food (the "unconditioned stimulus")--they see it as an odd, laboratory phenomenon, something that is unrelated to everyday life, and with good reason: It is a contrived arrangement involving dogs, bells, and research assistants wearing laboratory coats in a country very far away, a long time ago. (Pavlov's classic book was published in 1927.)
In truth, however, classical conditioning is more prevalent than one normally appreciates. Seldom do people realize that the tasty appearance of unnatural-looking and pretty odorless foods like Twizzlers, lollipops, candy canes, and plastic-looking cakes (see photo at bottom) owe their attractive, incentivized properties to the process of classical conditioning. If one had never tasted these foods, or, better yet, were a baby that had never tasted anything like these foods, the objects would probably not look tasty at all. The sight of a candy cane, for example, may just as well be that of a plastic toy. The same holds true for other incentivized objects, such as the ashtray for the smoker, the bottle for the drinker, and the pipe for the professor (that is, the professor of year's ago).
Another, seldom appreciated aspect of classical conditioning is that, as sophisticated as it is, much of it is mediated unconsciously, beneath the horizon of our conscious awareness. The circuits in the brain that are responsible for classical conditioning are very different from those responsible for our episodic, autobiographical memories, memories that, at times, can be experienced consciously. Unlike other forms of conditioning, such as operant conditioning--where one, for example, performs an action for a reward--the conditioned response in classical conditioning (e.g., the cravings one experience when looking at a beautiful cake) cannot be suppressed at will; they are 'involuntary.' One can suppress behaviors but not the urges associated with them (Morsella, 2005, Psychological Review), especially if they are due to what Pavlov discovered, a long time ago.