Students should understand how TIME affects our observations of the external world. For example, if they view a particular phenomena for ten seconds/30 seconds/one minute/ten minutes/30 minutes/one hour/one day/week/month or year, their observations are apt to vary greatly. While at times, it is necessary to generalize from brief observations, students should be cautioned about the danger inherent in accepting snap judgements of persons who visit a place briefly and then proceed to speak about that place as instant experts. Unfortunately, much of the popular travel literature is of this genre, thus severely limiting its use for teaching, when one reads literature attempting to describe other places, it is always wise to keep in mind the old saying; "one swallow does not a summer make!" Nor does a single story, film, game or meal or other brief experience – regardless of how exciting or memorable – tell us a great deal about another nation or culture. Over-generalizing from inadequate or limited data is a common human failing; allowing it to go unchallenged in classrooms, however, is a disservice to students.