As far as humiliation goes, if someone is totally delusional about their own ability, and isn't getting the hints that performing might not be the best idea, then *something* is going to have to burst their balloon. At that point, it becomes an issue of whether it's going to be their spouse or friend who sits them down and says "Look, you just aren't very good at this" or if it's going to be the public humiliation of an audience.
As far as money or time goes, the lack of talent can be less of an issue, if it comes down to an issue of someone neglecting their family or spending money they don't have. I could see it being a problem if someone wants to quit their job to write a novel or go on tour, but at least then you can use the practicality argument - even the most talented writers don't start out making a living on their books, so it's better to keep your day job until after you've sold a few books.