For me, it WAS 1995-96 Upper Deck Electric Court #310, David Robinson. A copy of that card was the ONLY card I ever had and no longer did. for some stupid reason I traded it away the day I got it...(I was in 5th grade at the time) and couldn't find another one until January of this year, when Database member Jason German sent me one. You can read my story about that one in more detail HERE.
Currently, I'm chasing some cards that I should have gotten in factory sets, and didn't:
1992 Langenberg ARCA Flash #101 & #106
1991 Thunder on the Water #15
And three cards, from one set, that I should have gotten in a hand-collated set I bought in the late 1990s, and didn't:
1996 Collect-A-Card Corvette Heritage Collection #D-88, #89 & #90.
A card that's just really proving hard to find for me is the 1991 Maxx Promotional Sample. (Probably not actually numbered P1, but until a copy can be located, who's to say?) 1991 Maxx is one of the most important sets to me personally, and it's the only card I need to have everything- a "Master Collection"- including, nearly, in packaging. (Missing only the factory set, which sells for $5, so I could grab it easily)
Interestingly, there is no NBA card that has been eluding me for a long time, now that I have the Robinson. Sure, there's some I don't have and would love to have - the 1986-87 Fleer Jordan and 1996-97 Topps Chrome Kobe Bryant are two that come to mind. But they are not hard to find. I could find multiple copies for sale at any time. I just won't pay that much for a single card. Sad story- when 1996-97 Topps Chrome was new, I bought a pack for my best friend at the time. He got the Kobe and wouldn't trade it to me, not even for money, which stunk because we both knew he didn't care about the hobby like I did. (His entire collection was from my duplicates). It irrevocably hurt our friendship. And then, circa 2003...I bought a set advertised as complete. The price I paid for the set was for the complete set- but the seller kept most of the rookie cards. (He missed a few that he wasn't apparently knowledgeable enough to know were rookies, as they were not labeled in that set, or just didn't care about- he actually sent me the Priest Lauderdale, for example). It's the only time in 18 years of buying over the internet I've bought cards and didn't get them (discounting, of course, the sealed factory sets that were missing cards). I never got my cards or my money back.
VERY slow trading due to health problems. Not transferrable so safe to trade with, just moving is painful and can't always access the cards.
Cardboard History My COMC
New Collection Website: Cardboard History Gallery (Still under construction)
Tips on how to make your scans look like the card does in hand (No more washed out, fuzzy scans!):