Post Hoc Ergo Propter Hoc
The Fallacy
Thinking that because Thing A happened before Thing B, Thing A caused Thing B.
Why it's wrong
Just because you did something right before a good thing happened, doesn't mean you caused it. It could just be a coincidence.
Example
I washed my dad's car, and then the sun came out. Washing cars makes the sun come out!
What the Fallacy?! (ELI5 Edition)