When you give the player a rare but powerful item which can only be used once but is never really required to proceed, most players will not use it at all, because they are waiting for the perfect moment. But even when this moment comes, they will still be reluctant to use it, because there might be an even better moment later. So they keep hoarding it for a moment which will never come. 

In the end, they will carry the item around until it is outclassed by other, more readily available resources, or even until the very end of the game. That means that such one-shot items don't provide any gameplay-value at all. They are simply too awesome to use.

What can you do to encourage the player to make use of their one-shot items and not hoard them?


Question: Currently taking graduate course as an Undergraduate
Answer: 
  In order to get a good chance to go into graduate schools for Math in Canada and USA, do I need to get a A or A+ in graduate courses as an undergraduate?


I don't think anyone cares too much about the distinction between A and A+, since the standards for what merits an A+ vary so much between universities or even individual professors.


  Or, is A– alright?


This is a little more meaningful, but it's not likely to be the deciding factor.  If you have a great application otherwise, nobody will care about an A- or two.  If your application is not so compelling, getting straight A's won't help much.  This could make a difference, but it's really a low-order effect.