Sometimes simple things in life becomes so complicated that you end up feeling miserable and whatever you think about is depressing and then you start feeling so terrible that you are sure that there is no light at the end of tunnel. Most of the times you come out of these situation and then you discover that all those worries have become sweet memories.
Sometimes in life we have lot of fun and we enjoy a lot over a long period of time then finally something terrible happens, and then you figure out that all that happiness was based on lie. From that moment all those nice experiences becomes a nightmare and you start re evaluating all that happened.
Some other times you have a terrible run. You are made to suffer a lot over a long period of time. You suffer so much that you start thinking "what is the point". Finally you realize that you have achieved a greater Happyness at the end of all misery. From that point all those miseries becomes sweet memories.