Definition: One thing is held to cause another, and it does, but it is insignificant compared to other causes of the effect
The object or event identified as the cause of an effect is a genuine cause, but insignificant when compared to the other causes of that event. Note that this fallacy does not apply when all other contributing causes are equally insignificant. Thus, it is not a fallacy to say that you helped cause defeat the Tory government because you voted Reform, for your vote had as much weight as any other vote, and hence is equally a part of the cause.
Identify the much more significant cause. (Cedarblom and Paulsen: 238)