It will depend on the objective of the campaign, but advertisers know they will never be able to get phil specifically. What they can do is shrink the target group to a much more relevant group. So instead of going after every male, 18-25, they can go after every male 18-25 who likes cars, videogames, lives in the Midwest and has an interest in sports.
They still want to get the best bang for their buck, the more targeting you apply, the pricier the CPM becomes (cost per thousand impressions). There won't be much of an ROI if you go after just phil the cost of doing so will make it pointless. But if you go for a wider range target with relevant interests and what not you will get a better outcome.
If they are trying to sell trucks, they target site content where they know their audience will be, and not the user specifically. If they know that 18-25 sports fans who like videogames will be on IGN and Xbox Live, that's where they will put their ads. There's a bunch of different types of buys an advertiser can make to meet their goals, each will have different costs and methodogy. Never does an advertiser expect 100% of their audience will be in one place.
I can do Behavioural targeting, which will target based on user habits. I can target by Re-targeting, serving ads based on previous sessions on a site (ie. build a car on an auto site, you will see ads for the car you built). I can do a blanket buy, males 18-25, or I can go with real time bidding which basically just buys any inventory for dirt cheap, but this inventory will usually suck.
Believe it or not, advertisers are aware of privacy, and more and more clients are also pushing for it, hence why stuff like ad choices (which is by no means mandated, and entirely voluntary) are taking off and gaining momentum. www.youradchoices.com
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