A logical fallacy in which it is assumed that because one thing happened after another, the first caused the second. Also known as post hoc ergo propter hoc. The problem here is that correlation does not equal causation.

Example: "I walked under a ladder, and two minutes later a meteorite hit my car! So walking under a ladder is bad luck!"

To prove the fallacy, show that the correlation is coincidental. Showing that either the effect would have occurred even without the cause or the effect was caused by something else is a good way to go about this.

If it were "I walked under a ladder and got hit in the head by a paint can", the walking under the ladder may in fact have caused the paint can to fall on your head. But it's still not bad luck.