Just before this resignation, I thought I was slightly or even way behind (the AI says I am wrong). I have only a few pockets of secure territory, a larger base on the left (not sure if he could monkey jump in) and a weak group on the right, while he has all four corners and a lot of potential in the centre.
This looked even to me (again, the AI says I am wrong). Despite my massive superiority on the left side, he has influence on most of the rest of the board (and was 5 kyu stronger at time of resignation).
At higher levels, do most Go games reach counting or end by resignation? (I know for chess, most games end by resignation.)
In my opinion, a 12 kyu isn’t “far stronger” than a 17 kyu, at least not on OGS and certainly not if the 17 kyu is essentially a provisional rank. You were already at about (at least) 14 kyu OGS level when you started the game.
Also, players in the DDK range have a bad habit (imho) of resigning before the game is really decided – at that level we all suck, and anything can happen until the territories solidify.
being distracted by other things (another game, visitors showing up, etc)
having to do other things (work, etc)
feeling they are behind and don’t want to finish the game
If you want to know why a player resigns, just ask them.
I suspect a lot of them don’t bother to answer.
All we - posters to this thread - can do is speculate.
Only the resigning player can tell you why.
Mostly your current rating and looking at your game results. I imagine your rating might settle higher than 14 kyu, or not at all, if you keep improving, but for now it seems a reasonable estimate.
By the way, keep in mind that you mostly learn by playing. If you believe you lack the specific skills needed to win a game, that might be all the more reason to keep playing so you can learn something about those skills.
Though I understand that it might be more uncomfortable to make that decision in correspondence games. But on the other hand, in correspondence games you can even make some research about those skills, which for me personally is where the educational potential of correspondence games lies, and why I’m sad that correspondence doesn’t fit in well with my life.
On first sight perhaps the game might have looked even-ish when white resigned, but on closer inspection, black has no problems while white has multiple problems to fix (A, B, C and D in the diagram below) with only 1 move to fix those. If white was aware of some of those problems, that might have been the reason why they resigned.
Your opponent happened to appear much stronger than you at the time (I guess 10k vs 15k?), but his rating is very volatile, so in reality the strength difference may have been much smaller. More like them ~12k vs you ~14k, which is not that big a difference.