> When did we have to stop waiting for crops to grow?

When we started producing more than basic things like food that are heavily dependent on the environment. In the knowledge-based economy, the only thing that meaningfully stops you from producing continually is you collapsing from exhaustion. However, even if you never got tired, you can still only produce so much per second, if you will, which caps your total productivity. That is the human limit; probably a fundamental one.

Only a tiny, tiny fraction of the population have to wait on crops growing now in order to offer that productivity. And of them, like myself, we can now do other productive things while we're waiting. I, for one, work in the tech industry when I'm not farming. Today, 96% of farmers in the USA are productive off of the farm in at least some capacity. Whereas, historically, farmers were busy trying to survive when they weren't being productive on the farm. Many a day were spent in the bush chopping wood so that they didn't freeze in the winter, for example.

Productivity can keep increasing beyond the human limit, but we have achieved that by introducing more and more non-human workers. Humans are already at the very top of their game, at least as we know it. 18th century farmers probably thought they were also as productive as humanly possible, so who knows what the future holds, but for now we have no idea how to make humans even more productive than they already are. Hence why their measure of human productivity is no longer increasing.

This was recognized a long time ago. It was the basis of the "go to college to make more money" script you may be familiar with if you are old enough to remember. It was well understood way back then that relying on human productivity gains was a dead end. The thinking was that colleges would enable people to move away from work and into leveraging automation, where productivity is effectively unbounded, with college research labs having played and still playing a pivotal role in that, but somehow along the way that got twisted into "go to college to get a job", so here we are... Now people spend god knows how much money to go to college to get the same job, at the same pay, that they would have gotten anyway. Which is pretty hilarious, but also sad.