An act of excessive simplification; the act of making something seem simpler than it really is

A simplification that goes too far (to the point of misrepresentation)

The fallacy of the single cause, also known as complex cause, causal oversimplification, causal reductionism, and reduction fallacy, is an informal fallacy of questionable cause that occurs when it is assumed that there is a single, simple cause of an outcome when in reality it may have been caused by a number of only jointly sufficient causes.