I believe in code re-use. You believe in code re-use. No-one wants to re-invent the wheel, especially not if there is a really great, aero-dynamic, ultra-fast wheel available.
That’s why we use libraries and components. But those libraries and components are not written by super-humans. They are written by people like you and me – people who make mistakes.
You’ve visited a building where you need an access card. Without the card, you don’t get in. But the card doesn’t (or shouldn’t) open all doors once you are in the building. Some areas must be off-limits. That’s physical access control.
Digital access control works on the same principle. It controls who can access the system, and what they can see once they are in.