What are the common pitfalls of the Singleton pattern?

Short answer: Global state: Singleton can lead to hidden dependencies and make testing difficult. Tight coupling: Other classes depend on the Singleton instance, reducing flexibility. Concurrency issues: If not implemented thread-safe, it can cause race conditions. Resource contention: Singleton might become a bottleneck if overused in concurrent environments.

Real-world example (ShopNest)

ShopNest payment fees use Strategy: IFeeCalculator with UPI/Card implementations chosen at runtime.

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.