"Aim high. If you dream it, you can achieve it." People tell kids that thinking it is doing them a favor; but in reality, it is doing them at best, a disservice, and at worst, harm. More on that in a minute.
The world is a cruel place. Being optimistic about it doesn't change this fact. I know, I know; I sound like a pessimist. But ask yourself this; If you want something, do you ever consider that there are roughly 7 billion people on Earth today, and even if only one tenth of one percent of them *also* want that thing you do, that means you are up against 7 million other people?
In other words, and in the truest sense, the odds that you will succeed are not in your favor. In fact, they are not even a 50/50 chance. The odds of individual success are stacked overwhelmingly against you. And yet, when it inevitably happens, we are surprised at our failure.
The world is not a child's drawing with a smiling sun and a rainbow in a clear, blue sky. For an interesting pseudo-experiment, ask a small child what made the rainbow in the picture they drew. Most won't know that before a rainbow can form, there must be enough of the right kind of moisture, which is produced by (cue the "dun-dun-DUN! music here) a storm.
They don't know it because we don't teach them that. We teach them that everyone is their friend (except old people, as one recent study shown, children will often pick old people to form a "stranger" mental image), and there will always be friendly ways to get what they want.
This, of course, leads me back to the first point. How is it doing them a disservice? Because it is a flat-out lie. It does nothing to help prepare them for life, in fact, if they believe it, it also hinders their mental development.
Now, I'm not saying we should be telling children that life sucks, then you die. Rather, I feel we should set our emotions aside, sit children down, and calmly help them understand that yes, there will be times when you fail. Probably many times. But it doesn't mean that you will fail every time.
There was a great line in the beginning of "Indiana Jones and the Last Crusade;"
"You lost today, kid. But that doesn't mean you have to like it."