Since every person has a unique background and unique experiences, each person will react differently to each message. This isn't to say that we don't react similarly to certain messages, but each reaction will still be unique.
As an example, consider the popularity of certain shows on television. The television networks know that a large group of people will enjoy a particular show, but that another large group will not like it. The show's creators try to include as much content deemed appealing by society to make the show likeable, but even fans of the show will like and dislike certain aspects more than others.
Take a show like American Idol. Although it began its 2008 season with over 37 million people watching (according to Nielsen), people within that fanbase had differing opinions about who should win. Depending on each fan's musical tastes, geographic location, age, and gender, they will like a particular contestant more than another.
Another example is the media coverage of political candidates. Since most people don't meet directly with politicians, we receive the information about them through the media - television commercials and debates, websites, newspapers and magazines, radio addresses, etc. Since we all have different backgrounds, different needs from society, and different points of view about the direction we want society to go in, we'll each pick the candidate that most matches our point of view about the world.
People use their individual skills, beliefs, and experiences to construct their own meanings from media messages.