Retargeting is the advertising you show to people who already interacted with you: visited the site, watched a video, started a quiz without finishing it. Instead of looking for new people, you bring back the ones who already knew you. It's almost always the cheapest and most profitable traffic you can buy.
The reason is simple: the vast majority of visitors don't buy on the first visit. Not because they aren't interested, but because they got distracted, weren't ready, wanted to think about it. Without retargeting those visitors are lost. With retargeting you find them again a few days later, when the moment might be right.
It costs little because you're talking to a warm, small audience. You're not educating strangers: you're nudging people who were already halfway there. For AsteNow the bottom-of-funnel retargeting reached 5,230 landing page views at €0.066 each. Those are the typical numbers of this layer: high volume, very low cost, because the audience is already yours.
Retargeting only works if you have something to restart from, meaning traffic coming in and a way to track it. You need the pixel installed from day one and a steady flow of visitors from the top of the funnel. Retargeting doesn't create demand: it collects it. It's the last part, not the first.
What to show returning visitors: not the same ad as the first time, but a step forward. To those who saw the page but didn't leave a contact, show proof, a case, a number, a real review. To those who started the quiz and didn't finish, remind them to complete it. Each segment deserves a different message, because it's at a different point on the path.
The mistake is treating retargeting as a separate campaign, detached from the rest. It's actually the last link in a system: cold traffic bringing visitors, a funnel converting some of them, retargeting recovering the others. Without the first two, you have no one to recover.
If you don't know whether your problem is bringing traffic or converting what already arrives, the free 2-minute audit on this site analyzes the 4 layers of the engine and tells you.