I enjoy multiple streams of passive income.

A woman wrote a technical manual in 2011 and it still sells. Every spring she spends three weeks updating it. For the other forty-nine she does nothing at all and money arrives anyway.

Passive describes the timing rather than the effort. The work happened — it happened years before the payment, which is a very different thing from not happening.

It also explains why the first stream is so much harder than the fourth. Nothing is arriving yet, and there is no evidence whatsoever that the thing being built will ever pay.