It's the basis of federation. Think of it like regular SMS. You can try to send a message to someone, but if they have their phone switched off or blocked you, they won't receive it.

[–] Derproid@sh.itjust.works 3 points 1 year ago

I'm not hugely familiar with how federation works or why it works the way it does, but why is this better than say instances only hosting what is put on their instance and the browser fetching from multiple instances? So when I want to view something posted on instance A with my account on instance B, instead of instance B keeping a cache of the post my browser just fetches the content directly from instance A?

[–] jcg@halubilo.social 5 points 1 year ago

Well, all the instances kind of acknowledge the originating instance as the OG and it's also the relay. For example, this reply goes from my instance, to sh.itjust.works, to your instance. If sh.itjust.works defederated from my instance you wouldn't see this at all even though you're not on sh.itjust.works.