Suffering - It teaches humans which guide they must follow.
You think I am cruel? No, it saddens me to say so, but humans need to suffer in order to understand. When a messenger from heaven appears – someone who can enlighten them on the direction to take – not only do they turn a deaf ear, but they often persecute them. And when a criminal comes along who will lead them to disaster, they welcome them, they cheer them on and carry them to power – it is they themselves who provide the criminal with the means to destroy them. So, it is clear: humans need to suffer in order to understand once and for all to whom they must listen and whom they should follow."