I am going to explain how something gains value.
Have you ever noticed when you were young and you have a cool toy that nobody else has and you appreciate it and cherish it. But then your friends get that toy as well and you start to lose interest in it.
This is because you can show it off to friends and brag that you arethe only one that has it.

In the real world items lose value like this aswell , for example :

[ Register or Signin to view external links. ] :Diamonds are quite rare thats why they are so expensive.
[ Register or Signin to view external links. ] :Coal isn't rare , but is getting rarer so it's gaining price.
[ Register or Signin to view external links. ] :Pearls are rare found deep in the sea in Oysters.
[ Register or Signin to view external links. ] :Oil is getting harder to find and is getting more expensive because its so difficult to find and even harder to drain.
It is also believed to Oil lubricate the earths crust and core or whatever and draining it can cause anarchy.