I guess we have to define effective. Is it effective from the consumer point of view? That might be a long discussion, and we might assume that a world without advertising might be the most effective way to live your life, etc. But is it effective from the advertisers' point of view? Unless you want to call 5+ million marketing teams around the world total idiots, you have to assume that they are meeting or exceeding their ROAS targets and therefore pouring a lot of money into Facebook.

> It just means that Facebook is good at selling ads, whether they are effective or not.

Facebook doesn't sell ads. Marketers choose to sign up and spend money, because their jobs depend on being able to achieve ROAS targets. Contrary to popular belief, the world of marketing is very quantified and apart from experimental budgets, most of the money is spent on channels that are proven to work.

But without getting any deeper into all of this, I think I found my answer - it appears that at least a subsegment of people on HN believe that over 100BN of ad dollars (25% of overall digital ad market) is spent on Facebook in an unprofitable way, and that 5 million marketing teams get away with it, year after year. Hence, it's possible for Facebook to achieve great financial results without their ad platform being effective.