Can you explain how DI containers resolve dependencies at runtime?

Short answer: DI containers use reflection to inspect constructors of requested services, resolve dependencies recursively from their registrations, apply lifecycle scopes (Singleton, Scoped, Transient), and build the full object graph to return fully constructed instances.

Real-world example (ShopNest)

Patterns in ShopNest should solve a real pain (swappable payments, test seams)—not be added for decoration.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.