It depends, as for someone who had to move out of his country because of war, a lot of songs, smells, pictures remind me of happy and peacefully we used to live and it makes me so sad.
however, some other times some stuff remind me of times i hung out with people or when i traveled to places and it makes me smile from my inside !
I've come to hate the feeling. Because it always turns to sadness no matter how happy I was initially. I end up thinking about what would've and could've happened but never did because I was un-motivated.
!