It's not this systematic progression of important things that you end up missing. It's the random crap that you never would have thought twice about back in "the day", whenever that was for you.
I remember back in college, when the Baptist Student Ministry was pretty much a bunch of guys and my friend Sunday (a girl), and then a rotating cast of guests. One of my friends was named Jonathan, but somehow he got the name "Jonatello", and then it was shortened to just "Tello". He was 26, the age I am now, and when he would hang out with us, he would be hilarious in this semi-creepy way. We began calling him "Creepy Uncle Tello"... I forget the exact moment, but it always made me chuckle.
Now, whenever I hear the word "Uncle" or the name "Jonathan", I think of Creepy Uncle Tello, and smile.
I can think of a thousand more important, more memorable things to be nostalgic. Yet, it's the stupid stuff I remember most, like the way my friend Steve would refer to flirting with a girl as "reaching out", and how we still refer to each other as "Mr. Reach Out" or "The King of Reaching Out", even though back in college we were pretty much perpetually single (I think we each had girlfriends for a couple of months at some point during my time in college, maybe).
Or even the memory of waking up at my friend's apartment with a cat in my face, or the time we put a temporary tramp stamp on another friend of mine at their apartment. Or all the times I'd have foam noodle wars with the youth group I led, and destroy them even though it was 4 or 5 on 1.
I feel like I did more important stuff, like this stuff shouldn't be what sticks in my memory. I played music in front of thousands of people, and saw kids give their lives to Christ, and graduated College, and did a bunch of other important stuff that should stick in my head. I wish I could remember that other important stuff, but I can't. I'm too busy remembering the time a little girl named Heather sat on me, and the other kids there asked me how that made me feel, and I told them it made me feel "a little under the Heather".
Nostalgia doesn't make any sense. That joke was freakin perfect though, you should have been there.
4 hours ago