The fallacy of the single cause 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.
If it is said that “A causes B,” it is rarely that B is caused only by A, but usually, there are other things that cause B simultaneously with A that are not explicitly mentioned. Assuming that only A causes B from the statement without further consideration is the single-cause fallacy.