We built the feature in two days. Making it reliable took two weeks.

The feature worked:
Button clicked
Data saved
Response returned
Done.
Then production started:
Duplicate requests
Users refreshing mid action
Slow external systems
Partial failures between workflows

Code was working.
System behavior was not.
Most development time is not spent building the feature.
It is spent making sure the feature keeps working when real users, real data, and real systems hit it at the same time.

This is something we deal with constantly at BrainPack. Building the feature is usually the easy part. Making it reliable inside existing enterprise workflows is the real work.