This topic is motivated from this question: Why is leave-one-out cross-validation (LOOCV) variance about the mean estimate for error high?
The top answer starts with
Oct 2015. My original answer here was irrelevant, as pointed out in the comments below and in a couple of downvotes. I replace it with a new answer now (but save my original answer below).
This is a complicated topic, and I must admit that I don't have a full understanding of it.
This question has 11 up-votes, and it is arguably not a good answer. The user himself is saying that the original answer was irrelevant and that he "does not have a full understanding of it".
I am myself a newcomer, yet I still think answers should be up-voted by veterans, to avoid misleading answers. Or a mechanism for too popular questions' answers to be up-vote protected.
This post was to warn about a problem I see: misleading up-voted answers, answers that might be up-voted by beginners because they like it or empathize with the answerer saying "This is a complicated topic, and I must admit that I don't have a full understanding of it", or because they see an easy to understand answer, or whatever reason. And I think the problem comes from the original question being a hot topic.
Disclaimer: I do not think that the answer provided should be deleted, I just find misleading that it has that amount of up-votes when, in my opinion, does not answer the question, which is exactly
"Is there a mathematical formula, visual, or intuitive way to understand why that average has a higher variance compared with the k-fold cross validation?"