物以稀为贵的英文：
When a thing is scarce, it is precious.

参考例句：

"When the fruit is scarcest, its taste is sweetest"
物以稀为贵

A thing is valued if it is rare
物以稀为贵

In the conventional world of supply and demand where we all grew up, value came from scarcity
在我们大家生长的这个传统的供求世界里，物以稀为贵。

when是什么意思：
conj. 在…时候；在…之后；一…就；考虑到，既然；虽然，然而
adv. 什么时候，何时；在那时；当时
pron. 什么时侯；何时
n. 时间

Tact is the art of recognizing when to be Big and when not to be little
知道何时应该宽宏大度,何时不应量小器微,是谓练达

Time flies when you are online.
上网的时候时间过得飞快。

When you see him, book!
当他见到他时，迅速离开！

thing是什么意思：
n. 东西；事物；衣物；财物；形势，情况；事业；家伙；事情

These things will happen.
这种事总要发生的。

These are things that were proposed as reasonable things to do.
这些被当作合理的事情提议出来。

Example is not the main thing in influencing others. It is the only thing.
榜样是影响他人的一样东西，但它不是主要的。

scarce是什么意思：
adj. 缺乏的；稀有的
adv. 仅仅，几乎不

Translation is a potentially scarce item.
译作是潜在的稀有商品。

Ration citizens when supplies are scarce.
当物品供应缺乏时，按定量配给市民。

Food and fuel were scarce in this region.
这地区食物和燃料都很缺乏。