Oh wow, let's not send food or aid to other countries then, but mirrors and an instruction manual written by this guy. Sure it will make a world of difference.
Grieving over a lost loved one? Ignore counselling, all you need is a mirror! Girlfriend dumped you and you feel down? Just smile and it will all go away!
He should sell the idea and make millions!
Oh wait...it's all BS, and whilst it may make you feel slightly happy in the short term, does nothing whatsoever to alter the situation or reality long term. It's a band-aid, a silly, worthless band-aid and the kind of useless "advice" that would be given in the 1950's, ya know, that whole "Turn that frown upside down!" nonsense.
Positive thinking *does* work, not saying it doesn't, but only in conjunction with other remedies and assistance. Simply saying "I will not be sad" and pulling faces in front of a mirror is as farcical as it can get and won't remedy anything, else I am sure doctor's might, ya know, have hit on it as a sole treatment years ago.