What the Fallacy?!
Affirming the Consequent
The Fallacy
Assuming that because the consequent is true, the antecedent must also be true.
Why it's wrong
An error in formal logic where if A causes B, and B is observed, one incorrectly assumes A must have happened. However, B could have been caused by many other things (C, D, or E).
Example
If it rains, the streets will be wet. The streets are wet, therefore it must have rained.