Left and Right Folding over an Infinite list

Question

I have issues with the following passage from Learn You A Haskell (Great book imo, not dissing it):

One big difference is that right folds work on infinite lists, whereas left ones don't! To put it plainly, if you take an infinite list at some point and you fold it up from the right, you'll eventually reach the beginning of the list. However, if you take an infinite list at a point and you try to fold it up from the left, you'll never reach an end!

I just don't get this. If you take an infinite list and try to fold it up from the right then you'll have to start at the point at infinity, which just isn't happening (If anyone knows of a language where you can do this do tell :p). At least, you'd have to start there according to Haskell's implementation because in Haskell foldr and foldl don't take an argument that determines where in the list they should start folding.

I would agree with the quote iff foldr and foldl took arguments that determined where in the list they should start folding, because it makes sense that if you take an infinite list and start folding right from a defined index it will eventually terminate, whereas it doesn't matter where you start with a left fold; you'll be folding towards infinity. However foldr and foldl do not take this argument, and hence the quote makes no sense. In Haskell, both a left fold and a right fold over an infinite list will not terminate.

Is my understanding correct or am I missing something?