First, nobody is saying they're discontinuous. But there are plenty of continuous results we can see that are concave up, i.e. they require commitment beyond a

First, nobody is saying they're discontinuous. But there are plenty of continuous results we can see that are concave up, i.e. they require commitment beyond a certain point to be more effective than not implanting them at all. For example, let's say initially we build a single road from coast to coast in the US, starting with no roads. There wouldn't be many places to drive to, there would be a small market for cars, and as a result of lacking economies of scale, cars would be expensive. There wouldn't be much infrastructure for purchasing or maybe even extracting gas, so that would be more expensive too. The road probably wouldn't get used much, and wouldn't be worth it. But if you build a bunch of roads all over the country between where people want to go, eventually they'll become worth it.