Now this is question I am honestly not too sure about.
I can well remember my Mum telling me "You chieve anything you like in life, if you put your mind to it". For some reason, that has worked badly against me - it wasn't Mum's fault, but it is a dictate that does harm some people; unfortunately, I am one of those.
A very young child, when something is repeated to him/her enough times, takes it as 'read' - what he/she has been told becomes a truism.
Not every child has the same mental attributes; experiences in early years can influence their characters greatly. For some, experiences of repeated failures leave them feeling very un-competitive; I know - I am like that. As I have said, no one is directly 'to blame'; not my Mother, not me, just plain old happenstance, repeatedly knocking a message into me - try as hard as you will to please everybody:- "it jut ain't going to happen".
I know it sounds far fetched, but there is another little aside to this, of which I have been told, and I must admit to not having studied it enough to be able to form an opinion. Young children listen to their parents intently - after all, Mum and Dad are the 'Guides' we first have. But kids don't have the ability to interpret meanings into what they are told.
The belief of those who advocate the negativity of this system would say "Tell a child he can achieve anything he wants to in his life, and you run the risk of screwing him up".
This is based on the premise of non interpretation by the child; he/she accepts the dictate as 'carved in stone' - it becomes a perceived truism, instead of a myth.
"I want to become a fighter pilot in the air force" - Andy, my own son told me, countless times; when it came to it, because of his vision (myopic), he would never have been accepted. For him, had I coached him with the "you can......", there might well have been a backlash of "Well, I can't, Mum & dad told me lies." - subconsciously.
We are, as far as the people who advocate this aspect of Neuro Linguistic programming, far better off saying "Try as hard as you can, and you stand the best chance; you cannot do better than your best - if you have done your best and still fail, then don't take it badly."
Reminds me of "If you can meet with Triumph and Disaster
And treat those two impostors just the same;.......................
...............................
Or watch the things you gave your life to, broken,
And stoop and build 'em up with worn-out tools." (from Rudyard Kipling's "IF")
Sorry if I have rambled, but this is something I feel needs more awareness.........