[janalsncm]

I believe the context for that quote is that it was referencing TV ads, which makes sense. How can a TV advertiser know who is watching?

Online ads were supposed to fix this problem.

[candiddevmike]

Ad attribution is extremely difficult across any ad medium, especially while respecting user privacy.

You may see an online ad two weeks ago and buy the product today, how do you attribute that?

[carlosjobim]

You use promotional codes for attribution, then you have complete knowledge. So it's extremely easy, and a solved problem. No need for analytics, no need to infringe on privacy.

[plorkyeran]

I watch a youtube video and the youtuber shills me some product along with a promo code. A week later I decide to buy the product, but I don't remember what video had the ad or what the promo code was so I just don't bother with it. How are you going to attribute this sale to the youtuber?

[carlosjobim]

In those cases you can't attribute, but that's okay. With normal ads you have zero certainty of attribution.

[8note]

If you can figure out the attribution, I'd say you've infringed on privacy.

You know what the buyer was looking at

[carlosjobim]

That's not an infringement of privacy in any way. Likewise then you know what the buyer purchased, since you sold it to her.

And nobody is forced to use a discount code.

[kyleyeats]

That quote's from around 1900 but your point stands for print. Nielsen actually got really good numbers for TV using statistics, self-filled form sheets and crisp one-dollar bills.