When you recite the figures of pi, 3, 1, 4, 2, ... it goes on for ever, and no-one seems to object to the "..."; Wittgenstein turns it around, by reversing the sequence he places the infinity in the present, a potential infinity becomes an actual infinity and most people find that disturbing. But infinity has nothing to do with time, it is outside it, so our discomfort being time-direction dependent illustrates that we should have been disturbed by the "...", in the first case -- this is Wittgenstein's brilliance.