Here's the direct answer: you find out by checking the layers in order, not by changing things at random. Ads fail at one of four points, nobody sees them, people see them but don't click, people click but don't convert, or the wrong people are doing all three. Each of those has a different cause and a different fix. Most wasted ad spend comes from fixing the wrong layer, usually the creative, when the problem was somewhere else entirely.
Work through the layers in order
Before changing anything, find out where people are actually dropping off. Every ad platform shows you this, and the sequence matters more than any individual metric.
Layer one: is anyone seeing it?
Check impressions and reach, in Meta Ads Manager for Facebook and Instagram, or in Google Ads. If these are very low, the problem isn't your ad at all, it's delivery. Common causes: your budget is too low for the platform's algorithm to leave its learning phase, your audience is so narrow there's almost nobody to show it to, or your bid is uncompetitive for the audience you've chosen.
Worth knowing: platforms genuinely do need a minimum volume of data to optimize. Very small daily budgets often produce misleading results, not because ads don't work for your business, but because the campaign never got enough data to find anyone. If you're spending a few dollars a day and concluding ads don't work, that conclusion isn't reliable.
Layer two: are they clicking?
If people see it and don't click, that's a creative and hook problem, and it's genuinely fixable.
The most useful test I know: show your ad to someone for one second, then hide it. Can they tell you what it was about? If not, the ad isn't being seen even when it's technically being shown. On Facebook and Instagram especially, people scroll past anything that looks like an ad, stock photography, text-heavy graphics, product shots on white backgrounds. Those blend into the noise people have trained themselves to ignore.
What actually helps here: lead with the problem rather than the product, use images that look like real life rather than advertising, and make the first three words do the work, most people never read past them.
Layer three: they click, and then nothing
This is the most common and most expensive failure, because you're paying for every one of those clicks.
The usual culprit is a break between the ad and the page. If your ad says one thing and your landing page headline says something different, the visitor has to do the work of connecting them, and most won't. Whatever your ad promised should be the first thing visible on the page, in similar language, not buried three scrolls down.
Beyond that, the common landing page problems are consistent: the page talks about the business rather than the visitor's problem, the call to action is vague or hidden, there's nothing that makes acting now feel necessary rather than optional, and the page asks for too much commitment too early. Someone who clicked an ad thirty seconds ago is not ready for a long form or a sales call, they're ready for one small, low risk next step.
Layer four: the right people, or just people?
Sometimes everything above works technically, impressions are fine, clicks are fine, the page is clean, and it still produces nothing. That usually means you're reaching people efficiently who were never going to buy.
This shows up differently by platform. On Google, someone is actively searching for something, so the intent is already there and the risk is bidding on terms that sound relevant but aren't. On Facebook and Instagram, nobody was looking for you at all, so the audience you selected is doing all the work.
Cheap clicks are a warning sign, not a win. It's entirely possible to pay very little per click and get nothing back, because the audience you bought was never the right one. The number to watch isn't cost per click, it's cost per actual customer.
The layer almost nobody checks
Here's where most ad advice stops, and where the real problem often sits.
Every fix above assumes your message is right and just needs better execution. But if you were never clear about who you're for and why they should choose you specifically, no amount of creative testing produces that clarity. You can optimize an unclear message indefinitely. It stays unclear, and you keep paying for the privilege.
This is why some businesses test for months, rotate through agencies, rebuild landing pages, and still get nothing. The ads were never the problem. They were just the most visible place the problem showed up, and the most expensive place to keep trying to solve it.
The honest test: can you state, in one sentence, who your ad is for and what specific problem it solves for them? If that sentence doesn't exist, the ad is guessing, and every optimization is a guess about a guess.
What to do instead
Work the layers above first, they're real and they're worth fixing. But if you've done that and the results still don't come, stop optimizing and go upstream. Ads are a distribution channel. They amplify whatever message you give them. If the message underneath isn't clear, more budget just distributes the confusion faster.
That's the difference between running tactics and having a system. Tactics are things you try. A system is your positioning, your message, your ideal customer, and your channels all pointing the same direction, so that when you do run ads, they're amplifying something that already works.