I suspect most people (HN people) hold pretty strongly the belief that everything can be quantified. However, within reasonable limits and current stats and science, lots of things in practice cannot - yet at least.

A lot of advertising probably falls under this. To verify effectiveness we'd need, as the article notes, to control for so many other factors that it would often be too difficult.

So we often guess, or leverage past knowledge and apply it to what we hope are similar circumstances.

If you take the point to be that marketing is not a hard-science, than it's true. Some cases sure, but plenty not.

That last part is the part you can't say definitively unless you have a lot of data, which is the point of the article.