Davidson and Riley in American Scientist:
Imagine that you are dining at a familiar restaurant, and you order a new item on the menu—something that you’ve never tried before—and later that night you become violently ill. What caused you to get sick? Your illness could have been caused by a touch of the flu, a familiar food that was poorly preserved or prepared, an exposure to a toxin, or a favorite cocktail interacting badly with some medication taken earlier in the day. But even if you are aware of these and other alternative possibilities, there is a high probability that you will blame the novel dish for your illness. Indeed, the taste, and even the thought, of that new menu item may subsequently make your stomach turn, and you may decide never to eat that food again.
No doubt many of us have had this type of experience. Why are we so quick to place the blame for sickness on a novel-tasting food instead of blaming many other equally plausible possibilities? You may be thinking that blaming the unfamiliar food is the most logical response, but why does it seem that way? We’ve eaten new things many times before without becoming ill, and we’ve become ill before without eating anything new. What makes the connection between a novel taste and illness so strong that it can override these other types of experiences? Answers to these questions, as well as evidence for the reality of the phenomenon itself, were found not in anecdotes but in the results of experiments. Those results shook the foundations of psychology as it existed at the time, and led to a paradigm shift in thinking about how humans and other animals learn in general, and about the conditions under which learning occurs.