The Truth.

 Spoiler

The world sucks and it's made up of people who are self-serving. Self-preservation is animal instinct. First comes your needs and then when you've had your fill, you might give to other people. This should be one of the first things that people learn so that they don't get swindled or conned by other people. Otherwise you won't be given any opportunities, period.

College courses for instance are mostly graded on a class bell curve. This basically means that if you are relatively smarter than your classmates, your grades will be around a B/A. If you are relatively dumber than your classmates, your grades will be around D/C. In harder classes, the competition can get brutal as everyone wants to get higher grades. This is because we often associate higher grades with success and a better life. Hence self-preservation.

If a child isn't aware that other children want the same things they do, work as hard as they do, and may compete harder for them in order to get it, then they will be screwed. Even wolves have a theory of mind and acknowledge that other animals have sentient thought processes that dictate terms for survival and self-preservation. This is what allows them to coordinate within the pack (coordination) and corner other animals (flanking movements).

If you're afraid of other people being jerks, then you are screwed. Because other people will come and take everything from you, if you don't fight back.

My thought is that by learning that the world is brutal after you've become good in something, would mean you will fight for what you've worked so hard to get to already. Instead of thinking "Hey, not worth doing," people rather think "Goddamnit, I'll do it anyways. I've wasted so much time on this already, so no need to stop now."

The second reason I want people to experience that the world is a cruel place instead of being told, is because you'll notice the effects of it. By being in a car crash, chances are you will be using a seat bealt. It won't be that efficient if you get this told instead, because "Well, it happens all the time, but not to me". And most likely it won't. But when it happens...

Are you saying that option A is telling the truth having the person die and option B is lying to save the person's life? Because I would go for option C or D, there is always another way. Just like lying is a way to get around telling the truth, there is a way to get around telling both the truth and a lie.

Well, that really depends. Let me give you an example.

Take the standard Kantonian issue: You're alone at a café, enjoying you ice coffee. Suddenly, you see a bloody man running from an alley, who starts to run down the road. Some minutes later, a person with an axe/gun/[weapon of your choice that will take the life of the guy you met earlier] runs out of the same alley, looks around, and then suddenly asks you: "Did you see where the person coming from this alley went?"

Now, usually you would have the following options:
- Lie, and say that he went some way he didn't.
- Speak the truth, and tell him that he went down the road.

You could eventually do an option C here, and tell them "I do not want to answer that question," but you'll probably guess what's going to happen if you do so.
Trying to get away from the question is essentially the same as lying (You don't want to answer the question, but you do not tell them that, as you would in option C), at least from my point of view. And I consider that, obviously depending on the question, as okay in some cases.