Day 21: First time you sold some of your D&D books - for whatever reason.
After playing D&D off and on for nearly 35 years, I sold my first D&D book last year. I had never sold a D&D book before that...and I still haven't sold any of my D&D books. I frequent gaming stores and am always looking for new ones. Gaming stores are like treasure vaults to me; its fun looking for hidden treasures in them. Around last year I found some older 1E books for very cheap in some of these stores. While I already had them, I still bought them and resold them on Ebay.
So, while I can say I have sold some D&D books, none were from my own collection.