What does "husband and wife are invisible" mean in fortune telling?

"Husband and wife are invisible" = "It is difficult to get married with others" = "The marriage character is not ambiguous".

* invisible:

No trace. "Historical Records" Volume 117 Biography of Sima Xiangru: "Those who cover the Ming Dynasty are far in the bud, and the wise avoid danger in the invisible. 」 ?

Abstraction without form. After the hit-and-run accident, his conscience and morality suffered intangible pain. 」