It's just data, is my point. Events are harder, require actual processing.

I'm really curious what you think is so hard about Twitter.

As far as I can tell it is basically a CRUD app with some real time analytics to surface some trends.

You said some stuff about Events bubbling, like if I Retweet something you seem to think there's a lot of complexity there. But as far as I can figure all that does is create a new row in a database somewhere and when someone who follows me fetches their feed, my new retweet gets included in there.

Aside from the scale, what's hard about it? Am I completely missing something?

"Aside from the hard part, this seems easy".

Is this even the hard part anymore? In 2006 maybe, but nowadays it seems like scaling is pretty solved. I always feel like scaling is more just expensive than hard.

I mean, you can make things easy for you and just choose GCP and use Spanner instead of trying to build your own from scratch, but that doesn't make the problem itself easy.