First digging your own grave was considered a virtue. Then custom; then unwritten law; then maktoub as Law.
It was a sign of honor and great virtue to dig your own grave. The Great dug their own graves, and all the citizenry aspired to be Great.
And each citizen was good about it. Generally. He’d set some time aside, before he died, to dig the grave. It would get dug.
Usually. Sometimes he didn't do the duty. Perhaps it became something he tended to put off until late in life (after all, if he dug his grave too soon, he’d have to go keep going back to make sure the grave stayed dug, as another person, or nature, might tamper with it).
Sometimes he managed to die before it got dug. In that case, some family friend or descendant would sneak in and dig the wayward grave before anyone found out (as digging your grave was a sign of honor/virtue, not doing so would be a source of familial embarrassment).
In general the Great were good at it too, perhaps actually better, it being a sign of Virtue and all. But sometimes the Great said, “I’m too busy. If I forget to do some Thing, you understand,” etc. So it got be done anyway, as it was Law. Maybe bought, but done, and since the Great gave life to the People, the People got it done. Reliably.
De facto there was now a government, there to get things done reliably. And perhaps economics. As if a well-dug grave inspiring government wasn’t bad enough, maybe it should also start money.
Remember, stories are our best revenge.