"What are the core security objectives of any system?"

Three letters. One of the most common interview questions in cybersecurity.

CIA.

Confidentiality - only authorized people can access it.

Integrity - data has not been tampered with.

Availability - systems work when you need them.

Every security control that exists serves at least one of these three objectives.

If you cannot explain why a control exists in terms of CIA, you are not ready for the interview.