Ask HN: WRT Doing things that don't scale – How do I validate a SaaS idea?

So it's been repeated to death. Don't build your product until you validate your idea has strong product market fit. To do this, you should do something that doesn't scale, like set up a web page and do the work manually, like DoorDash.

OK, but what if the idea can't be validated like this because the whole value proposition is automating stuff.

To give specifics, I want to build something around setting up automated builds of Blockchains. I don't see how I can validate this idea without actually building at least some of the product first. Like, I can't manually mine blocks.

Am I over thinking this? (probably I reckon)