How can violating LSP cause issues in software design?

Short answer: Violating LSP can lead to: Unexpected behavior when a subclass does not honor the contract of the base class. Code that breaks at runtime when substituting a derived class. Tightly coupled code that depends on specific implementations rather than abstractions. Unit tests failing when testing subclasses in place of base classes. Essentially, it defeats the purpose of polymorphism.

Real-world example (ShopNest)

Open/Closed in ShopNest: add a new payment method by adding a class, not by editing a giant switch in CheckoutService.

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.