You do not own it, you only rent it is the crucial point, but it's buried inside a distracting outer point.

The distracting outer point is "Build what you Can’t Ship", which has limits, and is just another iteration of the old don't sell out idea about art. It's like saying "be an outsider artist". That's not a good goal. It's all very well spending years writing a book in secret - supposedly without a thought for the audience - but if you accidentally wrote it in a private language that nobody can ever read, or made it unrelatable or incoherent, then that's not creative brilliance, it just isn't any good. Without pandering to popularity, you should still write for some audience, and if you're making art at all, imagining an audience is inherent to that. Similarly if your software only runs on your own machine, or (referencing a recent HN post) you perhaps spent years writing an adventure game in QBasic for the love of it, but accidently made it 64-bit so nobody can run it on DosBox, well, that's suboptimal.

So another point is that writing for a niche market is a fine attitude. On the other hand all this you only rent it stuff makes the niches smaller and more obscure, and that's a bad thing. You want a comfortably-sized niche where there's a medium-sized audience, so you get some attention in return for being subject to only some pressure to perform and conform.