Why is lying a major sin?

As I and in all probability all of you know, lie or Kezb is counted as a major sin or in other word it is considered as Kabaer (majors) sin. But the question which I am looking for its answer is that what the reason(s) is that Islam declares this act as a major act? In other word, what is its negative point(s) which made it as a major sin and is there any hadith about its reason? *Note: both Shia and Sunni perspective would be appreciated.*