This is the part that gets me (you beat me to the reply, heh): So you buy a skateboard; then suddenly, your pages are full of skateboard ads. Then you buy a new set of wheels; ok, now your pages would likely be full of parts for a skateboard. Then you buy a ramp or something: Now you get all kinds of skateboard paraphernalia, safety devices, hell maybe some scooters.

Given these generous assumptions: * That all these purchases are trackable, by the same advertiser, with definite certainty * That you're even buying online in the first place, so you can advertised to * That you'd respond to advertising at all, because thus far their recommendations have been purely reactive, not predictive of what you'd buy * That an eventual purchase could be directly tied to the advertisers work

After all of that investment of time, money, and energy, if they somehow managed to secure a sale of say, knee pads, how much do they actually make? And how much did the knee pad company pay to acquire that lead which led to a sale?

My basic question is: How is any of this profitable? It seems like an absolutely massive ecosystem of enormous firms all trading money back and forth and trading data back and forth, to at best, make marginal bumps in otherwise happening sales.

This boggles my mind and I would love an enlightened HNer to weigh in if they happen to read this.