One of the less commonly known fallacies, which usually passes unquestioned, is the "argument by lack of imagination" or alternatively called "argument by ignorance";
To give an example of such argument:
Imagine that at year 1000 BC, two people had this little chat,
PersonX: I wish I can reach the moon.
PersonY: You are unrealistic person. It is impossible to reach the moon.
Obviously, PersonY lacks the basic element of imagination, therefore had made a false assumption based on his ignorance of the possibility to land on the moon.
One of the notable usuages of this kind of argument is in oposition to atheism; It is said that in the old times, this conversation happened between a religious person and an atheist:
Religious: Yesterday i saw a ship; It had no crew, it had no captain, it was sailing in the middle in the sea without anyone onboard!
Atheist: Sorry Sir, I think this is a made up lie!
Religious: So you are telling me that it makes sense that our whole world, with all galaxies... The accurate system in which a simple flaw can be drastic... This big big universe can exist without a captain managing it, yet find it questionable to find a ship without a captain?
Obviously, that religious person lacks the basic element of imagination! I leave the proof to the smartasses out there!! ;)
One of my school teachers used to say: "Imagination is more imprtant than knowledge"; I have to agree, because you can gain knowledge by imagination, while without the element of imagination you cannot make use of the knowledge you have!