Comment by Shreyansh Pandey on "What should we try to develop while learning as a backend developer?"

What you mention as concepts and skills are - in your example - equivalent.

Authentication and Authorization are concepts, but so are databases and REST APIs. Designing a secure role-based auth system is a skill. Similarly, designing a REST API which confers with the JSON:API standard is a skill. You get the point.

With that said, I would highly recommend you to take a project and then apply these concepts (on the top of my head):

Role-based or tier-based authentication and authorization;
Data structures based on volatility vs. immutability;
Server-Side and client-side caching;
Message Queues and their more-applied form: delayed response mechanisms;
Payment systems (this is a tough one)

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