nostalgia

"It's surprising how much memory is built around things unnoticed at the time"

I have always liked this saying. I seem to remember the tiniest details of the most simple moments. And at times can't even remember big moments that have occured.
What is it that makes a particular moment in time a still imagine in our minds?
I sometimes remember the journey more than the destination. A simple car trip, a simple moment.
I spend my time sometimes wondering 'am i currently creating a memory?' little insignificant moments at the time, such as a walk through the park can stay with you for the longest of times.
Is there a hidden message? What was so significant about a certain moment that the brain recognised? I find these unanswered questiong to be of a fascinating aspect.