>>He made a school yearbook on the internet and copied some features from existing social networks like MySpace. Facebook was just in the right place...
Well. That's the key point. Lots of people did social networks. Several had a lot if success with them. Remember circa 2007? FB was one of many. Zuck made a social network that (a) got and stayed popular (b) made no way and (c) successfully changed user behaviour. Before FB, social media was mostly anonymous and targeted at young, fringe or techno-elite online culture. FB are mass market.
I agree that VR is yet to be seen, and that fb's ability to execute is dubious. But, Zuck is more capable than most/all CEOs of social media seen this far.
Twitter us more if a lucky shot.
It remains true though that social media, generally, is not technically demanding. That said, the demands of scale complicate that. Look at Amazon and aws.
There aren't many fb-scale tech companies out there. It's not competition in an infinite field. It's competition in a field of one.. or perhaps three. JPMorgan or Berkshire Hathaway aren't going to beat them at this game. If it's a matter of beating other mega scale tech shops, it may be just a matter of executing better than not executing.
Competition at the ground floor (say series A) is brutal. Even if you're brilliant, you probably need a great strategy and greater luck. Competition at the mid range is meaningful. A Zara, Boots or OnePlus or whatnot still need to beat other players. At the FB/google level... there just aren't enough players. They don't necessarily compete at all, against other players. Products can succeed or fail, but it's not about head to head abilities. Where competition actually exists, like azure/aws, at best it's usually a field of 2 or 6 possible competitors with a chance of outside disruption. They're not in a "beat restaurant in town" game.