> That doesn’t work because we’re assuming that most marketers are making easy mistakes. The playbook is so simple that people on HN could write it, supposedly.

Those are someone else's words, not mine. I never argued that winning on Facebook is "easy" (and for the record, neither is it on Google). It's not easy, it's just doable. And for those who have the skills and resources to do it, it's massively profitable. I would even argue that if you're letting an agency run your Google or Facebook account, you're lacking the resources to do it right. What you need is top-level talent competing against your nearest competitors, and winning battles inch by inch. An agency will never give you the talent you need to go up against a company that just raised $100m and is running their performance marketing in-house (and if you don't have such a competitor, then you're either smarter than anyone else in the world, or simply not pursuing a VC-investable market).

So no, it's not easy at all. But it's doable and totally worth it.