Why is facebook so successful?

I agree with Sean Parker's decision to advertise facebook after it reaches a big amount of users because than they wont turn "The Facebook" into a social network that has small amount of members and it is crowded with ads. So what they did was when they had a lot of members they released ads. I think they actually did the right thing. Some people say that they should have had ads earlier but that my have screwed the whole business. And also i would rather wait a bit and make billions , rather than have a chance to loose everything.Also their spreading process was very smart as well. They slowly spread it around. First in the States and than even in Europe. This made collages that already had a social network go to Facebook because they had all their friends from other schools there. Facebook is so successful also because Mark did the right website in the right moment , when the world needed that kind of social network. I think that some of the decisions he made weren't the best like screwing up Eduardo to get only 0.03% of the company but  he made the right decision believing Sean Parker. After Sean was arrested he was forced to leave the company and than Mark made Eduardo the Co-founder of Facebook and gave him his 7%. ( Eduardo's net worth is around 2.75 Billions). I think that Eduardo deserved more because without him Mark wouldn't have the chance to even create facebook because in the start Eduardo invested in the facebook , and with that money Mark was able to host the Website and to keep it running.