What resources did he have access to besides being a Harvard student? That's a huge one, but it's not like he had access to (or needed) lots of resources to make The Facebook a success at Harvard. And after that it was all downhill.
There are a ton more to keep going on.
I'm not saying the first versions of Facebook were ingenious feats of engineering, but Mark easily may have never learned to build things. Considering everything else mentioned in this thread, we can reasonably conclude that a lot of went very right for him at many points along the way.
2. Being white
3. Being cis
4. Being straight
5. Being born in the US