One I’ll always remember, was my first trade.
I was 7 years old when me and my little brother were just zapping through channels on TV when we were intrigued by a boy throwing a red-white ball at a caterpillar (end of episode 2), and we were hooked on Pokémon since.
About 1-2 weeks later our parents bought us both our first Pokémon booster pack, unlimited edition English Base Set. Both of us pulled a holo, my little brother an Alakazam and I a Chansey.
A few days later I showed them to friends and other kids on the school playground. One of the older kids asked if I would want to trade his Vulpix, Pidgey, and Pidgeotto for my Chansey. As a kid I only cared about more cards, and didn’t care about holos much at all, so a 1 for 3 trade was a no-brainer for me, and I immediately accepted.
Later that same week I was downstairs when my parents were watching the 8 o’clock news, and they also mentioned how the Pokémon craze took the country by storm. They also mentioned how some cards were worth about 100 Gulden (old Dutch currency) adult collectors were willing to pay, and they showed a Charizard, and.. you guessed it, a Chansey.
At the time, I had no idea there even were different versions like 1st editions or Shadowlesss, and I doubt the news reporter did either, but because of that news message showing the Chansey, I still remember that first trade I did to this day.
After that I’ve been more careful and thoughtful about trades, for a kid at least. 
I’ve also bought that Chansey for like 3 bucks 5-6 years ago (as well as a Reverse Foil Legendary Collection Moltres, another card I once traded away), for nostalgia sake. 
Greetz,
Quuador