Michael Kaminsky uses Plato's cave to explain why ROAS and other marketing metrics are shadows, not truth. Incrementality, the actual sales lift from a campaign, is what matters, but it requires comparing two impossible realities at once. A clean 4.2x ROAS feels true enough to build budgets on, even when it's nowhere close.
Chapters
In the allegory of the cave, Plato describes a group of people who'd spent their entire lives chained inside a cave facing a blank wall. Behind them, a fire casts a shadow of objects onto that wall. The prisoners watch the shadows move. They give them names. To them, the shadows are reality. It's all they've ever seen. Now think about your marketing stack. Every tool you use, your ad platform, your analytics suite, your attribution model, is showing you a shadow. It's a projection of something real, but it's not the real thing. That real thing is whether your marketing actually caused a sale. That's called incrementality, not who converted after seeing an ad, but who converted because of it. Incrementality is the one number every marketer needs to know. The only problem is that no dashboard can show it to them directly. That's because measuring the true incrementality would require seeing two versions of reality at the same time. One where you ran a campaign and one where you didn't. Then comparing the difference. You only ever get to live in one of these realities, so every measurement tool is doing its best to estimate what the other reality would have looked like. That estimate is the shadow on the wall. And here's what makes the shadows dangerous. They look like answers. They seem to us like reality. A dashboard that showed you nothing would be obviously useless. You'd ignore it. But a dashboard that shows you a clean 4.2x ROAS? Well, that's convincing. You build plans around it. You defend it in meetings. You allocate real money against it. And the number alone can't tell you whether it's close to the truth or completely off.
