“What you end up remembering isn't always the same as what you have witnessed.” 

nostalgic memories typically entail cherished, personal moments, such as those spent with loved ones. Those memories, in turn, inspire positive feelings of joy, high self-regard, belonging, and meaningfulness in life.While certain smells or sights or touch evoke nostalgia, less obvious triggers—borne from the mind rather than the environment—Often the causes of  are more mental than physical. A bad relationship, poor self image, a history of abuse, stress, frustration and many other factors can change your overall attitude towards life which may directly impede your overall performance. Such tendencies are deep-rooted in mind and nurtured by excessive Negative Emotions.

 Nostalgia, then, seems to be one way that people cope with various negative mental states, or “psychological threats.” “We see nostalgia as a psychological resource that people can dip into to conjure up the evidence that they need to assure themselves that they’re valued.”

Nostalgia is like a grammar lesson: you find the present tense, but the past perfect! 

 nostalgia is shown to be both a driver of empathy and social connectedness, and a potent internal antidote for loneliness and alienation. It serves to remind you of what intimacy you have achieved and therefore what you are capable of. nostalgia helps build resources like optimism or inspiration or creativity, which are correlated with mental fortitude.