The longing is an affective experience very special. It differs from other emotional states that can only be felt in the past. You can not feel nostalgic for things present or future. Another feature is that it is a state of ambiguity. On the one hand feel pleased with what you remember. On the other feel displeasure at not being able to enjoy the present.
People can miss many things. It may be mentioned a loved one missing. An old love relationship may also wonder. And it may be a place, a time of life, etc. Can result in a lot with the nostalgia. It is not uncommon for there prevails a state of sadness and decay that make it difficult to live the present.
That is the reason why you do not want to have it. Many mistakenly believe that the cause is to remember the past. And again this is the who bears the blame. It is thus the point that some try to fight to block the memories of yesterday. That does not stop being a fairly radical move. And I could also say that rather artificial. There are grounds reason to believe that not a good idea. Before giving any suggestion in this regard I would mention another feeling. Comes up because shares attributes with longing. It is an unpleasant feeling and it only feels for things past. I'm talking about remorse. Again, the solution proposed to combat it is to forget the past. It sounds easy, but another thing to do.