What are you talking about? Should planes stop flying when they encounter an error?
Safety critical systems will try to recover to a working state as much as possible. It is designed with redundancy that if one path fails, it can use path 2 or path 3 towards a safe usable state.
Startups. When you are not sure how to map data relationships yet, MongoDB is the best tool. You can easily build a prototype without worrying about the database.