What factors prevent you from getting a complete, unbiased picture of world events from news media?
1) Reporters can't be everywhere. Journalist Walter Lippmann wrote: "All the reporters in the world working all the hours of the day could not witness all the happenings in the world. There are not a great many reporters. And none of them has the power to be in more than one place at a time."
Simple economics prohibit many stories from being covered: It costs too much to maintain bureaus in or send reporters to all the places where news that might affect you could take place (anywhere on earth). In addition, some governments ban or otherwise hinder news coverage in some areas you might like to know more about.
2) Even if reporters could be everywhere and report on everything, you can't read or view all they report. Your world view is inescapably shaped by whatever perspectives you choose of the news sources you follow.
3) In viewing events, there are as many perspectives as people. Remember the story of the blind men and the elephant? Each described the elephant differently because each was touching a different part - the trunk, the tail, the ears, the legs.
It's the same with news events. No matter how fair and complete a reporter might try to be in his coverage, he cannot look at events from any other perspective than his own, colored by his own past experiences and personal beliefs.
And if a reporter tends to be a bit careless, or is under deadline or space pressure, his story, as one editor says, may "show very little originality or effort to come at the same subject from a different aspect and look at another dimension."
If you are not at an event halfway around the world, and if you don't fully understand that event's background, what the media report, for all purposes, is that event, at least to you. The picture is not complete, but what other perspective can you take?