Nostalgia is a longing, a sentimental look back to a time when things were at least perceived as better, and this usually happens when the present time is unhappy or depressing.
The nostalgia in Bruce Springsteen’s song “Glory Days” talks about two friends, one thinking about his glory days of high school baseball pitching prowess, and the other about the days before her broken marriage when she could turn the head of any guy. The lesson Springsteen speaks to in the song is that nostalgia is a trap that is a waste of time.
And I hope when I get old I don’t sit around thinking about it