It is a reference to a magician's trick - he shows you something (for example, coins) and makes them disappear, saying "now you see them, now you don't". This has become a set phrase for trickery or deceit.
It is a reference to a magician's trick - he shows you something (for example, coins) and makes them disappear, saying "now you see them, now you don't". This has become a set phrase for trickery or deceit.