I'm watching Sunday afternoon U.S. football on television, and there's no football without commercials. In the case of the game I'm watching, the commercials are primarily for beer and the television network's new shows. The purpose of the commercials is to get you to buy the products or watch the shows. Endless effort and enormous expense goes into the commercials--who they're targeted to, what their messages are, and what they look and sound like.
The problem is that no commercial, no matter how good, will help your products and services to survive first contact--the point at which the customer actually buys the product, uses the service or watches the show. Movie studios have learned that the hard way. Heavy advertising and promotion increase the odds of getting a good opening day--at which point advertising ceases to be effective, and word of mouth takes over. If viewers love the movie, they'll text message their friends and tweet about it, and ticket sales will increase over the weekend. On the other hand, if they hate it, they'll send out text messages and tweets, ticket sales will go down over the weekend, and then collapse the following week.
The same thing happens every day in every product category. Advertising can stimulate the first purchase or the first viewing, but it can't get people who didn't like it after they tried it to buy more, nor can it stop them from telling their friends, acquaintances and followers. That's why your focus should be on the buyer's first experience with your product or service, not the effort to get them to buy it in the first place.
That may sound dangerously like the "build a better mousetrap" argument, but it's not. I'm not saying that you don't have to do promotion, but rather, the far more important thing is your customer's first experience with your product or service. The reason is that word of mouth is becoming the driving force for future sales of just about everything, and unhappy current customers equal fewer future customers. If you've got a restaurant, your food and service had better be good. If you're selling cars, the cars that your customers buy had better be reliable, and when they need service, the service had better be good. If you're trying to get people to watch your new television show, that first episode had better be great.
Advertising and promotion won't help you to survive first contact with new customers, and it won't save you from bad word of mouth. All it will do is increase the chance that you'll make that first sale. The rest is up to you.