I think it's a bit nuanced, and maybe poorly explained by the original author, but to me, "left-pathers" are always "move fast and break things" to the point that whatever they build really only works as a throw-away prototype, and the effort to architect sensibly is minimal.

"We don't really need to use REST, we can just create some endpoints that have undocumented side-effects. We don't need to abstract vendor calls into a separate class, we can just implement that functionality directly in our endpoint code."

These sorts of decisions aren't actually materially faster, they're just lazier. And maybe that's "a sprinkle of QC"? But it's a lot of unforced errors that don't really save time to implement, and also create a lot of problems later on.

On the other end, with the "right-pathers", you can have people that really try to over-engineer at any opportunity. This is sort of typical of people who have worked in much larger teams. This can mean building out a k8s cluster when you're still a team of 2-3 people, splitting into 10+ microservices, deciding to use Kafka when a simple queue system would work, building out in-house load balancing for dubious reasons, etc.

The middle path is really something that resembles the "Best Simple System for Now" — when I've done this, I think about how I can solve a problem and not have to rebuild it entirely within 12-18 months.