This type of reasoning is fallacious because mere temporal succession does not establish a causal connection.
A logical fallacy of the questionable cause variety, it is subtly different from the fallacy cum hoc ergo propter hoc ('with this, therefore because of this'), in which two events occur simultaneously or the chronological ordering is insignificant or unknown.
[1] Post hoc is a particularly tempting error because correlation sometimes appears to suggest causality.
The fallacy lies in a conclusion based solely on the order of events, rather than taking into account other factors potentially responsible for the result that might rule out the connection.
"[3] The form of the post hoc fallacy is expressed as follows: When B is undesirable, this pattern is often combined with the formal fallacy of denying the antecedent, assuming the logical inverse holds: believing that avoiding A will prevent B.