The whole point of this article is that scale actually isn't such a complex problem. Like others have mentioned, the reasons Facebook and Twitter even though th

The whole point of this article is that scale actually isn't such a complex problem. Like others have mentioned, the reasons Facebook and Twitter even though they seem simple (i.e. CRUD for posts, what can be so hard?!), the simple social features of their service is a very small part of their tech, since in fact they are ads platforms and this is where the efforts are being spent. I remember the first time I saw the Facebook Ads platform, the Events Manager etc - it's a highly complex system that changes all the time. Many more engineers are working on that than on maintaining the ability to Reply to a post feature. WhatsApp, until Meta, had none of these things.