My mother herself admits that she and my father pampered my elder brother a lot more than they ever did me. And the guy turned out to be a dick, so you can understand why I tended to be resentful of him.
He bullied me mercilessly, and would give me purple nurples every chance he got. He sabotaged most of my ventures, and once even slipped a note in my collar before an exam that got me caught for cheating.
So when I became ruler of the world, the first thing I did was get him arrested and then tortured in amusing ways. Then I exiled all elder brothers to the moon. That sparked an outrage that I found sadly incredible. So it was the guillotine for every protestor.
The world’s infrastructure was affected for a while – I had underestimated the number of elder brothers in the world – and there was even an unsuccessful coup that I am sure could be traced back to this decision of mine.
The world soon settled down, and firstborn sons were executed whenever secondborns came into the world. And after some time, people with sons mostly stopped having secondborns. A few years later, we stopped provisions to the moon colony. I gave my brother a wedgie as a celebration.