I've heard people in games mention that the game is programmed so that when you really need an item the game will not give it to you. You only get items that you don't currently need.
I think this is BS and it's peoples minds playing tricks on them. What is the term for this kind of trick playing your brain does? It must be related to the awareness you have of a particular item when you need it and the anxiety associated with the situation every time you don't get it.