Have you ever faced issues with Singleton pattern in multi-threaded applications?

Short answer: Yes. In one project, a singleton was used without thread safety, causing race conditions when accessed concurrently. This led to inconsistent state and application crashes. We resolved it by implementing thread-safe lazy initialization using Lazy<T> in .NET, ensuring the singleton instance was created safely once, even under heavy parallel access.

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.