# Fast in the Demo, Slow for Users: Best, Worst and Average

Explain why a search that was instant in your demo is slow for users, name its best, worst and average cases, and see why Big-O usually promises the worst one.

![Cheat sheet: Fast in the Demo, Slow for Users: Best, Worst and Average](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/11/265a3f1033754bd1b3359ee6655984ff.webp)

- Category: Data Structures
- Level: Apprentice
- Tags: Average Case, Best Case, software-development, Worst Case
- Updated: November 3, 2026

Source: https://www.ask-codey.com/cheat-sheets/big-o-best-worst-average-cheat-sheet