In general the days of our life tend to run together with a few events that really stand out and stay crystal clear for years. I distinctly remember the day Elvis died and when the Challenger exploded and when my first son was born. Some things burn them selves into out memory so deeply that we don't just remember them happening but we remember what we were thinking and how we felt. The is nothing wrong with using the power of that memory as a yardstick to see how much you have changed.