Gods play games with the lives of mortals. Complicated games.
The god of the orcs read the base rules, saw it was a game of war, and built a race that was strong and tough, aggressive and fast-breeding.
The goddess of the humans built a race that was perceptive.
The goddess of the elves read the magic supplement and built a race that twisted the energies of the universe as naturally as breathing.
The goddess of the humans granted her race understanding.
The god of the dwarves read the fortifications supplement and built masters of stone, capable of living inside hollow mountains.
The goddess of the humans granted her race ambition.
When the quantum physics supplement was published, the gods agreed that it was badly written, and none of them made use of it.
The other gods said to the goddess of the humans, “You have barely looked at the rulebooks. Are you sure you understand this game?” But the goddess of the humans only smiled.
And the game began.
The orcs ravaged the countryside in great roving bands, until the humans invented swordsmithing and martial arts, tactics and discipline. And the orcs could ravage human lands no longer.
The elves built towers of pure magic, and laid enchantments over entire forests, but the humans devised wizardry and matched them. At first it seemed a feeble thing. A wizard needed a shelf of books to do what an elf could do with only a gesture. But no elf could match the powers of a full coven of wizards, supported by a well-stocked library.
The dwarves built impregnable fortresses of stone, stretching far under the land. For a time, things seemed at a stalemate. Then human metallurgists unlocked the true nature of steel, and the humans built fortresses taller and stronger than dwarven stone. And human chemists found explosives powerful enough to breach the dwarves' defenses.
The other gods cried out “Cheater! You have given the rulebooks to your creations! That is how they find all these exploitable mechanics!”
“Not so,” said the goddess of the humans, “I only gave them the power to discover and exploit the rules for themselves.”
By the time the humans invented nuclear weapons, it hardly mattered. They had already won.