The marketing world has changed. Previously we tended to assume a direct consequence of a marketing initiative on a consumer (hell, even proved it qualitatively and quantitatively), and the trick was to scale this as widely as we could. One consumer sees an ad we know they like, buys a product, therefore let's get as many consumers to see the ad.
But this view fails to take into account the interaction effects that take place. Other media influence the consumer. Other competitors. Other consumers. And in complex ways. A consumer can reinterpret the ad, having received a different piece of communication. With the advent of social media this phenomenon (which was always present, has become more prominent.