Occasionally when I talk with non-cubers about blindcubing, they ask "But how do you know you're done?". I find that quite irritating and I don't really have a good answer.
I agree that I also find this question irritating, it shows that the person is not really thinking about what they're saying. As Shelley said, it's even more frustrating when they ask it after you've already explained how a BLD solve works.
How would I *not* know? It's like asking how do you know you're done writing an email, or asking a question, or tying your shoes.
Wow I really like this, I might actually try to work this into my answer for this question! (I'm serious!)
It's like they think I turn randomly and have to see when it happens to get solved... I don't get it.
I've had a non-cuber who was in my class, who saw me cubing and asked me about it, respond that "we (non-cubers) usually just turn stuff and hope that we start getting some more colors together". I think that non-cubers can't see beyond this mindset, and they probably just assume that cubers are just "better" at doing this. It would be as if they think a cuber is using a super fast version of "trial and error" every time. I don't know if this is true, and I am inferring here, but it would explain the "How do you know when you're done?" question.
Your thoughts about how to reply?
Just like the sticker response I
always preempt this response. I know that 95% of the time I show speedcubing to a group that someone will make the sticker comment, so I make it first. I also know that probably around 95% of the time I either demonstrate or show blindsolving that someone will ask "How do you know when you're done?" so I explain usually something like:
"When I study the cube I'm not memorizing what it looks like, I actually have almost no idea of how the cube looks throughout most of the solve. What I'm memorizing is a list of directions that I must follow that will solve the cube. Once I get to the end of my list of directions, I have to be done, because there are no more directions to follow. At that point I put the cube down."
You will on rare occasion
still get the "How do you know when you're done?" question even after saying that, but it happens much less often.