Each HTTP request is independent and self-contained, so the server keeps no memory of previous requests.

After sending a response, the server has no memory of the client. Each request-response cycle is complete in itself. This means the server can't naturally track:

• Which user is making requests
• What they did in previous requests
• Shopping cart contents, login status, etc.

Cookies and sessions were invented to work around this limitation.

Cookies are key-value pairs the browser stores and automatically resends with every request to the same domain.

How they work:

1. Server sets a cookie via Set-Cookie header in response
2. Browser stores the cookie
3. Browser sends cookie with every subsequent request to that domain
4. Server can read the cookie values

Cookies persist across requests and browser sessions (until they expire), enabling stateful behavior over stateless HTTP.

Go deeper:

• Using HTTP cookies (MDN) — the canonical reference on Set-Cookie, the Cookie header, and lifetime/security attributes.
• HTTP cookie (Wikipedia) — origin of the name, cookie types, and the privacy/security landscape.