You and Lazare are right on the money. And the thing with the database is that the code that inserts/updates it has to agree with all the querying code about what the implicit schema should be - but it's implicit and scattered around your code - so on a large team it's very hard for everyone to understand that implicit contract and it's going to be a constant source of production bugs.

Schemas don't change that much compared to code, having a strict schema enforced by the database saves you so much time and pain and downtime in the long run.