You surely know Murphys’ law: Things will fail and errors will occur.

Use quality scenarios to document or specify what kinds/categories of such failures or exceptions your system handles or has to handle.

Examples:

• The system recognizes within 60 seconds if an external payment provider becomes unavailable. It will then notify an administrator within 60 seconds.
• In case of non-treatable application- or runtime exceptions the system will create appropriate logging events, that allow to diagnose the error, but do not contain personal user or account data (of data security category 2 or higher).