Twitter, Instagram, Youtube, and the like basically any information-sharing platform have made their founders billionaires in a very short time, so could someone found a system that could replace them.
Facebook took Bebo and MySpace market share. There was actually another video sharing website a few short years before YouTube but most of the world didn't have broadband connections / decent connections at the time.
The problem is the companies that will replace are in fact one in a billion. Their stars will align right. Like there are thousands of Facebook clones out there by people who had the same idea of being the next Facebook. They weren't.
It's Survivorship bias - We only look at, or even hear, those who are successful. But we never hear of the thousands (more even) who fail.
So to answer your original question of is it hard? - it is extremely hard. However, should you not try then it is impossible. But most of the companies that will become the next big internet thing have millions invested in them to grow. Again, Survivorship bias that we could focus on those three ex-google employees who set up YouTube from their garage.