Alas.

When approached by her sadly demented grandfather with a convoluted tale about a missing bicycle helmet that ended with his comment "...and so I figured you'd have it if you had it", the unfortunate Equuschick offered (without any malice whatsoever, only a misplaced sense of amusement) the reply "You're quite right, I would have it if I did but I don't, so I don't."

Somewhere this is probably written down in a collection of things not to say to those suffering from dementia.