Why Facebook is such a successful Website/Brand ?

Amazing question Mohamad.
In my personal opinion facebook is successful because it bends its ways to the user needs and it is easy to use.
Plus it has a lot of features that is useful for business and for individuals.

The reason Facebook became successful is because of it's ease of use and it's powerful privacy settings and security.
I am sure you guys remember Hi5, the reason Hi5 was not successful because alot of people found it complicated.
Facebook was developed using Ajax programming which is very light and easy to use by tech and non-tech savys!

The obsession with "moving fast" is an overriding theme for Facebook.
Moving fast means fast feedback, which means accelerated learning.
 Fast learning was vitally important for evolving the product and for scaling the site.
Key to moving fast is having frequent, small releases (minor updates up to several times a day, apparently).
Facebook is very good at risk management and exploiting variability.
 This has enabled them to innovate at an unparalleled pace.
Something Facebook has handled particularly well is decentralized control and alignment.
 One gets the impression that the whole staff is on a mission.
 The bootcamp program is instrumental in this.

Due to its security and features. And we made it populer.