Cost per click is the most discussed and least useful measure. A twenty-cent click that never buys costs more than a three-euro click that buys one time in ten. The only question that matters is the cost of acquiring a customer and what that customer returns over their lifetime. Until those two numbers are measured, you are not steering a campaign, you are watching it run.
So we always start with conversion tracking, before the first ad. A form sent, a call made, a quote signed, a sale: each event must be reported, with its value, and survive the disappearance of third-party trackers. That requires server-side collection and not only in the browser. It is technical, invisible, and it is what separates a steered campaign from an endured one.
Finally, the best ad does not rescue a bad landing page. Cost of acquisition is decided as much after the click as before: load time, promise kept between ad and page, short form, visible proof. We refuse to launch a campaign towards a page we judge to be losing, because that is spending your budget to prove something we already know.