What common mistake do developers make with Polymorphic relations, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Polymorphic relations, why does the mistake cause problems, and what is the safer approach? One recurring problem with polymorphic relations is applying it without understanding the boundary it protects. Declaring a relationship with the wrong foreign key or inverse direction and then debugging symptoms from queries that never matched the intended schema. In addition, Polymorphic relations allow one related model to belong to more than one model type through a type-and-ID pair. Safer engineering approach: keep the responsibility in the correct layer, use the framework's supported API, validate and authorize inputs, avoid hidden side effects, and verify the behavior with tests.