I'll bet that's it. I knew I'd seen this before. Well, good for you for telling your own joke, but naughty on you for not following the rules!

Though I'm sure you didn't make up the blind girl and the well one, because I heard it at an open mic just a few days ago. I suppose you both could have come up with it simultaneously, but it seems more likely that it's just in the world, out there, in our brains.