What is the reason so many people addicted to posting and spending time on facebook?

What is the reason so many people addicted to posting and spending time on facebook? – My take on this is that they just want to show off, although there are many other reasons, endless! but if we rate them or do a survey and the majority of the people will admit that just to showed off. Yes – off course there are already survey out there, but do you trust them? do you believe people are telling the truth?