the old man from the frontier lost his horse, how could one know it would not be a blessing; a setback may turn out to be a lucky break in the end

the old man lost his horse, but it turned out for the best; a setback may prove to be a blessing in disguise

Literally "how can a sparrow know the will of a great swan"; used to mean that common people cannot possibly understand the lofty goals or ambitions of a great person.