Here's why:
* Subject-verb agreement: The subject "this day" is singular, but the verb "was" is used with a plural subject.
* Word order: The placement of "you" is incorrect. It seems like it's supposed to be the subject, but it's misplaced.
* Meaning: The sentence doesn't have a clear meaning. It's unclear what is being said.
To fix this sentence, you need to rearrange the words and possibly add more information. For example:
* You gave the speech on this day.
* The speech you gave was on this day.
* This day was the day of your speech.