An old frontiersman loses his horse—a blessing in disguise. How do you know if it's an idiom?

This idiom can be explained separately.

An old pioneer lost his horse-a blessing in disguise.

Pronunciation is sà i w ē ng sh ē m, yān zhēfü.

The metaphor of the interpretation is that although you suffer for a while, you may actually benefit from it. It also means that bad things can be turned into good things under certain conditions.

With "a blessing in disguise is a blessing in disguise".