> But most system also ingest external data -- that data truly is "unknown" until you parse/validate it. Absolutely. And there are tools like Zod or e2e type s

> But most system also ingest external data -- that data truly is "unknown" until you parse/validate it. Absolutely. And there are tools like Zod or e2e type safety solutions to solve this exact problem. And otherwise that data will come in as `any` or already as `unknown` so there will never be a use case for `as unknown as B`. This only happens when the data has already been assigned a type (here, the type is A). Now you're working on recasting it to fix your mistake instead of fixing the core issue of the incorrectly typed data. The `A as unknown as B` workaround is only relevant when TypeScript believes A and B are so drastically different that they have nothing in common and shouldn't be cast as each other. The reason TypeScript believes that is either because it's true or because you made some earlier mistake. TL;DR: This article is about fixing your own mistyping and not about typing something that lacks any. It's not about the boundaries of your application but about the internal workings