If you maintain data records manually in Excel sheets, you tend to not “normalize” the data into several tables, because having to chase foreign-key references

If you maintain data records manually in Excel sheets, you tend to not “normalize” the data into several tables, because having to chase foreign-key references means you quickly lose track and don’t see everything related to a single entity in one place anymore. That’s because Excel doesn’t provide you with “joined” views. When inspecting a database interactively with a database GUI/TUI, this is very similar, unless you start building queries that lets you join the data together again (which is harder and less intuitive than just browsing tables and filtering/searching in them). Of course, not normalizing the data makes it more laborious and error-prone to keep things consistent, the more non-1:1 data associations there are. When databases are not presented as an interactive table-browsing tool, but as an application’s data store, where the application can join data as needed, then the benefits of having everything related to an entity “in one place” (in a single table) are outweighed by the drawbacks of non-normalized data. However, this is not obvious when you start out in the table-browsing paradigm. People naively tend to structure the data the way they would for manual organization.