People aren't paying attention to you. It takes much more than you imagine to penetrate their consciousness.
When you advertise in a newspaper, for instance, you've got to run your ad many times before your audience takes note of it.
You'll need to run the ad five to ten times for them to see it once. If it's a small ad, you'll need to run it more often.
Of course, seeing it once won't inspire action on the part of your audience—even when they have a need for your service. They'll need to see it many times before they take action. Some experts say they need to see it ten times before they'll call.
If you were running newspaper ads, that means that you might need to run your ad 50 to 100 times before you'll get the first call. Of course, newspaper ads have been subjected to a great deal of study since they've been around for a long time. Newer forms of advertising are still being evaluated.
However, the principle holds regardless of how you deliver your message: they (the audience) generally aren't paying careful attention, and it takes much more effort than you might imagine to get them to take action.
Some will argue that some modern forms of advertising are different. I don't think that's the case. Pay-per-click ads, for example, appear repeatedly in my browser before I click on them. I'll see them over and over before I decide to click. And, of course, once I click, I usually bounce right off the landing page without moving forward. It takes a tremendous effort to get us to act. We're hesitant, we're careful, and we're prone to maintaining the status quo.
If you're going to advertise, and certainly advertising works in many contexts, be aware of our tendency for inaction. Don't expect us to move quickly. Accept that you're going to have to communicate your message over and over to get our attention and get us moving. That's the way of the world.
If you're going to advertise, be realistic and give us time to respond to your call to action. Before you jump in, know that you're going to have to continue advertising for quite some time in order to recoup your costs. We need to notice you and then absorb your message before we act. That's going to take some time.