When is an Amendment not an Amendment, Sir?

Yaar samajh nahi aaya! I'm stuck between two seemingly similar concepts in Constitutional Law - the doctrine of Basic Structure and the concept of amendment to Article 368. Please help, sir. In Raghul v. Union of India (1971), the Supreme Court held that the Parliament cannot alter or abrogate the basic structure of the Constitution, including certain provisions under Article 368 itself. But here's the thing - what exactly constitutes a basic structure? It seems like a subset of the concept of amendment to Article 368, where the Parliament can amend any part of the Constitution including Article 368, but only with two-third majority and a ratification vote from half the state legislatures. But then, how can the basic structure be protected if it's already a subset of the amendment process under Article 368? Yaar, koi bat nahi aata!