Just to play Devil's Advocate:
As human adults that have lived their entire lives on the planet Earth (some assumptions there, but I don't think they are unreasonable!) don't we all have an enormous store of knowledge before we go "adventuring"? If I take a map and point to Australia, I would bet that instantly 10 or more details spring into your mind, regardless of where you are from. Similarly, if I say World War 2, I'm willing to bet you know many (if not all) of the major players, who was allied with who, some of the more (in)famous leaders and generals, and even a few of the major battles/engagements. If I say avocado or automobile, you instantly know I'm referring to a plant/food type on our world, as well as a major technological breakthrough that changed our civilization. However, I have never explored the Amazon rain forest, nor ridden in a submersible vehicle in the Mariana Trench, so those would be "adventures" for me, full of wonderment.
If you are looking at this from a character perspective and what a character would know, then you are making a lot of assumptions here. As a player, youare the product of a modern society with access to writing, a public education system that ensures that most people are literate, and technological advances in travel and di
Technology allows written material (e.g., pamphlets, newspapers and books) to be mass produced so that more people have access to the information. Once public education moved from just literate enough to read the bible to full literacy not being limited to the elite, more people had access to written knowledge without requiring knowing someone that could translate.
Meanwhile, advances in transportation technology allowed for exploration to far off lands (e.g. the New World) and the dissemination of information from these lands to to the Old World to be relatively (several months by ship). Radio and then TV and the internet have each increased how fast we get our information. Radio and TV also ensure that one no longer need to even be literate or have someone literate translate written information if they understood the language. So without the technology to reach the New World and either send back avocados physically or, at least a description or image, you would not have any idea of what an avocado was if you were living in the New World.
A good example of how important the written word is can be seen in Jared Diamond's
Gun's Germs and Steel when he discusses Pizarro's capture of Athullpa and their conquest of the Incas Their guns, swords, horses, and the diseases they carried were all important in Pizarro's conquest as were Native American allies (guns, actually, played a small part beyond psychological). However, the written word was also important.
When the Spanish arrived in Central American already had a body of written" knowledge human behavior and history" including some knowledge of the inhabitants of the New World. They had written accounts of Columbus's voyage to Hispanola and that of Cortex to Mexico. Therefore, they arrived in Central America with some knowledge of the technology and political organization they might encounter. By the time they had encountered Athullpa and the Inca, they already had experience fighting and conquering Central American socieities and more refined knowledge.
In contrast, the Inca had no previous knowledge of the Spanish when they encountered them or any other idea of the diversity of societies of the outside world beyond their sphere. Furthermore, while they did have a written language, but it was limited to relatively few. All Athullpa had to work with was a word of mouth account based on limited observation of the "Spaniards at their most disorganized". Based upon this limited knowledge, Athullpa and his men had been erroneously told that the Spanish were not warriors or a threat whom could easily be dispatched by a couple hundred warriors at best.
Now, granted, I went to two cultural extremes, but my point is that, from a Modern perspective, it is easy to forget that there are numerous factors that to our wide breadth of knowledge. In actuality, a lot of setting factors that will determine what is "common" knowledge in a given game and the reliability of that knowledge (in our world, for instance, there were texts stating that the mouths of Ethiopians ere located on their stomach). We also need to remember that without push factors (e.g., war, drought, etc.) or pull factors (e.g., economic opportunity) most people in settled societies supposedly never traveled more than ten miles from their home (soldiers, travelling merchants being among the exceptions).
