🍪 Understanding Cookie Behavior in Server Components (vercel#73001)

This is meant to add a bit more clarity of why we can't set cookies to
the browser in a server component even if it's through a server action
or route handler.

Co-authored-by: Delba de Oliveira <[email protected]>

docs/01-app/03-api-reference/04-functions/cookies.mdx

@@ -74,6 +74,15 @@ To learn more about these options, see the [MDN docs](https://developer.mozilla.
   - If it belongs to the same domain from which `.set` is called. Additionally, the code must be executed on the same protocol (HTTP or HTTPS) as the cookie you want to delete.
 - HTTP does not allow setting cookies after streaming starts, so you must use `.set` in a [Server Action](/docs/app/building-your-application/data-fetching/server-actions-and-mutations) or [Route Handler](/docs/app/building-your-application/routing/route-handlers).
 
+## Understanding Cookie Behavior in Server Components
+
+When working with cookies in Server Components, it's important to understand that cookies are fundamentally a client-side storage mechanism:
+
+- **Reading cookies** works in Server Components because you're accessing the cookie data that the client's browser sends to the server in the HTTP request headers.
+- **Setting cookies** cannot be done directly in a Server Component, even when using a Route Handler or Server Action. This is because cookies are actually stored by the browser, not the server.
+
+The server can only send instructions (via `Set-Cookie` headers) to tell the browser to store cookies - the actual storage happens on the client side. This is why cookie operations that modify state (`.set`, `.delete`, `.clear`) must be performed in a Route Handler or Server Action where the response headers can be properly set.
+
 ## Examples
 
 ### Getting a cookie