"Saiou ga uma" is a Japanese phrase that means "Saiou's horse." It's an abbreviation of "Ningen banji saiou ga uma," by which a famous Japanese proverb is known.
The literal translation is "All human affairs are like Saiou's horse". It basically means you can never really know what will prove to be "good" or "bad". The meaning came from a Chinese folk tale about an old man called Sai. Here's the story:
Once upon a time, an old man, Sai, lived near the Chinese Northern Fort. One day his horse ran away. His neighbors commiserated with him over his misfortune, but Sai said "How do you know this is not really good luck?".
A few days later the horse returned, bringing another horse with it. When his neighbors congratulated him on his good luck, the old man said "How do you know this is really good luck?"
Sure enough, some while later Sai's son fell while riding the horse, and broke his leg. The neighbors called it a misfortune.
But it turned out to be good fortune when all the young men of the village were ordered to join the Emperor's army. Sai's son didn't have to go because he had a broken leg.
Psychologists call this reframing. When you take an event and view it from slightly different circumstances, its meaning can change dramatically.