“Just because you can’t see something doesn’t mean it’s not there.”

Can you prove that fact to him? If your campaign generates results, you’ll have data to back it up. “We don’t run ads so that you can see them every time you go to your favourite websites. We run ads so *your customers* see them when they’re ready to consider a purchase. Here’s the revenue, views, and clicks over the past 90 days…”

If you can’t prove your impact, that’s a problem regardless. But surely you’ll have some numbers you can report to say, “your ads are running and people are seeing them”.