Zhuangzi was a famous philosopher in ancient China.
Once, the philosopher Zhuangzi was walking through the mountains with several students when they came upon a group of woodcutters resting beneath a massive, lush tree.
Zhuangzi came under the big tree with his students and asked:
"A tree this fine—why not cut it down?" A woodcutter replied, "This tree is good for nothing." Zhuangzi told his students, "Remember: because it was useless, it grew so tall and lived out its natural years."
Zhuangzi and his party came out of the mountains and arrived at the home of an old friend. The old friend was delighted to see Zhuangzi and ordered a servant to kill a rooster for hospitality. The servant asked for instructions:
"Of my two roosters, one crows at dawn and the other does not. Which one should be killed?" The master replied, "Kill the one that does not crow."
The next day, a student asked Zhuangzi, "The other day, the large tree in the mountain was spared because it was useless; yesterday, the rooster was killed because it was useless. Master, what situation would be safe?"
Zhuangzi smiled and said, "One should exist between usefulness and uselessness, seemingly right but not, so that no one can seize a handle." Later, the idiom "seemingly right but not" came to describe being between right and wrong, expressing ambiguous opinions.
Source: *Zhuangzi*, "Mountain Tree"
Meaning of the Idiom: Later, the Chinese idiom "似是而非" came to describe being between right and wrong, expressing ambiguous opinions.