Yeah, need a bit of imagination to walk there with me, but you are saying just use `saw_eclipse_at`. That would require having knowledge of the entity's birthday, the date that the event occurred on, and so on, which in this imaginary scenario, we do not.

I would not store that in a schema, storing bday and date seen is much more useful so that when the business inevitably asks for saw eclipse at 50 too you can answer the question without adding a saw at 50 boolean. Bday is also super useful info for a business that cares how old someone is (as your hypothetical one clearly does).

Often the stated requirements of a problem are far too specific. Part of the job is system design is saying no to suggestions and finding the deeper constraints.

This example is a great illustration of why booleans are usually a mistake.