Yes, it's an idiom No it doesn't have 'that' meaning ...specifically It sounds to me like a rip off of the much more common: "You don't know what you've got until it's gone" The meaning is exactly the same, and the original prevents any 'misinterpretations' :-)

it means: you don't realise the importance of something you have until it is gone but i like your interpretation too!!

:O maybe that is how you heard it, but it does not usually mean that... normally it means that while you can get something easily, you don't worry about it, but once you lose it you realise how important it is to you

You can not understand the value of something only when it is lost. In chinese , we also have this kind of proverb: 只有失去后才知道它的珍贵。

All the above answers are correct. What is interesting is that 李汉伦 rightly points out that there are different variations of idioms which have similar meanings but different wording. I bet that there is a similar idiom in Chinese and Arabic and Russian and ...... The list would be endless. Often the idioms or sayings are taken from an original source and then shortened. So "thumbs-up to all!