It's an article of widespread faith that data-mining enables advertisers buying online adverts to target consumers with laser-like precision. Vast warehouses of servers grind through billions of records of consumer profiles and transactions and with a bit of algorithmic magic, distill all this data down to the prime target audience for whatever good or service you're selling: probiotic goo, battery-powered back-scratchers, Zombiestra(tm), investment newsletters based on darts tossed by monkeys, etc.

And everybody knows online media is the place every advertiser wants to be and needs to be. By some measures, online advertising exceeded television advert spending in 2016 (around $70 billion each). Unlike traditional media advertising, which is stagnating or declining, online advertising is still expanding smartly--especially in mobile media.

Combine the promise of god-like targeting via data-mining with fast-growing online platforms, and you've got advertisers falling over themselves in their rush to spend billions more on online advertising.