Taken from somewhere else, this an an example
Event A: You start taking a new vitamin supplement.
Event B: You notice you haven't had a cold in a while.
Fallacious Conclusion: "The vitamin supplement must be the reason I'm not getting sick anymore."
Why it (in this comment) is a fallacy:
There's no proof that the vitamin supplement is the cause, just that it came before the lack of colds.
You could have simply been lucky, or the cold season might have passed.
It's possible that the lack of colds is due to other factors, not the vitamin.
Another example: because event Y followed event X, event X caused event Y