The hind that would be mated with the lion Must die of love. But somehow we missed it. The dance started with copying. Some molecules floating in the seas roughly 3,500 million years ago stumbled on the trick of copying themselves. Once they did, they multiplied and multiplied until there was no more food for new copies.
Resources are always limited.
So, soon after copying started, competition started. Millions of years passed. Through tiny copying errors accumulating over many generations, the structure of those self-copying molecules eventually diverged. Some of those variants were just a bit better at surviving than others. With the relentless competition for scarce resources, the tiny advantages turned decisive, and the slightly better self-copiers multiplied at the expense of the less fortunate.