A common backend mistake: treating database schemas like temporary code.

Code deploys in minutes. You ship it, watch it, roll it back if it's wrong. A schema doesn't work like that. The moment production data exists, the schema becomes the memory of the system — and memory doesn't roll back.

Every shortcut compounds:

The column you added as nullable "for now" still has three meanings two years later

The status value you retired still sits in a million old rows

The constraint you skipped in the app gets skipped by the second service too

So schema design has to consider what code design can postpone: relationships, constraints, future queries, data integrity. Put the constraint in the database, not just the validation layer — applications change, get rewritten, multiply.…