1-"This is not the first time I see this mistake."

2-"This is not the first time I saw this mistake."

I think one is correct because it is a fact. Which is correct? Am I right? And what's the difference in meaning?

The ordinals (first, second, third, ...) and only usually trigger the present perfect.

This is not the first time I have seen this mistake.

This is the second time that you have said that.

This is the only time I know of that Jane has refused to go with us.

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Neither of those. It should be "This is not the first time I HAVE SEEN this mistake".

Think about it like this.

I HAVE SEEN this mistake before. Someone else made the same mistake in the past.

I HAVE SEEN your mistake (I saw it just a moment ago, so I can use past tense, although I still SEE your mistake).

This is not the first time I HAVE SEEN this mistake.

It's wrong to say "SEE this mistake" because I can't still SEE the mistakes that other people have made, because that was in the past. So I need to speak in past tense, both for the other mistakes that I've seen in the past, AND the mistake that you just made. I've SEEN the past mistakes, and I've SEEN your mistake.

This is just my interpretation, anyone feel free to correct me

Hi Kris,

"Have seen" is not past tense, it's present perfect.

I disagree with your explanation to some extent. The present perfect in such a context can also be used for a present ongoing action as below:

Lisa is singing. It's the first time I have heard her sing. ---> I am still hearing her.

BUT you cannot say:

Lisa is singing. It's the first time I hear her sing.

It's simply an unexplainable illogical grammatical rule that we abide to.
Agreed, you can't say "It's the first time I HEAR her sing".

Thanks for the explanation. I'm not sure I understand completely. Someday I'll learn all the grammatical terminology but for now, I know what's right and what's wrong, but I sometimes have trouble explaining it.
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