A turned out harder than expected; B had challenges, some seemly insurmountable, some merely incredibly tedious. C looks even worse.
I'm exhausted, lost interest in D. But I "should" continue. I give up... a failure.
All because A, B, C make D "easy".
Had I wanted to make a game from the start I would most certainly not have made a language first! That would be crazy. And that's my comments about sunk costs -- just because I have Leaf, it'd still be crazy to do this other projects in it.
You could also call it a partial success. Your A and B may help others write their C and D.
Also, hobbyists should have the motto “the journey is the reward”. If you had fun or learned doing A and B, it’s not a failure, even if all the learning was “if you want a D, it’s not worth it spending time writing a slightly better A and B”.
(This is not a political comment! The saying long predates the current swamp drainers)