Is there some principal of nature which states that we never know the quality of what we have until it is gone?

Is there some principal of nature which states that we never know the quality of what we have until it is gone?

是否有一种自然法则说，我们永远不知道我们所拥有的东西的质量，直到它消失?

-- Herman Melville 赫尔曼·梅尔维尔