Do you agree "The first time people look at any given ad, they don't even see it." ?

No, i don't agree .

Good Ad will catch your eye from the first time. 

Frequency is only required for average ad .

Yup i do agree but not completely...
as per Thomas Smith its true that as per advertising approach The first time people look at any given ad they don't even see it.
Frequency and selection of media is very important to Grab attention of the user towards the ads.
In TV there is a possibility that you don't notice because the moment you realize this advertisement is different and want to convey some great message the ad is over which is not the case with Digital, Print and other medium...
So, to above statement i will agree 90 % to be true....

True.

 

This is why when an ad agency shows you your first preview you see it three times in a row before giving feedback on the ad.

It depends on the quality of your ad.If you think people will not look at it for the first time, change the visual.

It depends on the quality of the ad, there are advertisements that have taken the attention of people at the very first glance with the way it is projected with fascinating visuals, a clear message conveyed as to what the product aims to satisfy and the brand, everything projected so well in that given fraction of time.
that's where creativity of an Ad campaign comes into light! Though the people might not be able to capture everything at first go, but the second time it appears they wait to know more and pay attention because they know one thing for sure that this ad is interesting and unique!