The fallacy of the single cause, also known as complex cause, causal oversimplification, causal reductionism, root cause fallacy, 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.
Fallacy of the single cause can be logically reduced to: "X caused Y; therefore, X was the only cause of Y" (although A,B,C...etc. also contributed to Y.)