What are the limitations of the ‘circumstance’ I can choose to trigger the Contingency spell?


The contingency spell description states:

Instead, it takes effect when a certain circumstance occurs. You describe that circumstance when you cast the two spells.

There is nothing written that requires the circumstance is perceivable, in contrast with how you can Ready an action. It also does not limit the distance. It also does not limit the details you could come up with (since 10 minutes is pretty long time). Possible scenario on my mind:

When the King Leo XIII died. I wouldn’t have known since I’m so far away, but when the Message cantrip takes effect, whispering my previous Message, now I know he is dead.

I’ve just realized that this spell is insanely powerful and can be abused if not properly limited. What are the limitations, anyway?