@chuckwendig "Instances are like mail servers. When you log into Google, you send mail from Google. When you log into Microsoft, you send mail from Microsoft. When you log into your work account, you send mail from your work servers. Maybe your client may let you log into more than one mail server at once, but you have to log into each mail server locally. That's how federation works. You can have multiple local accounts and toot from each of them."
@chuckwendig At least, that's how I try to explain it to people. I have no idea if that's helpful, but that's the closest I've ever come.