User blog comment:ChishioKunrin/Volume 3 Episode 3 Sneak Peek/@comment-27087951-20151107205543/@comment-24891101-20151110071720

I liken it to personality. Lots of people exist across the planet with quite similar personalities (not that I'm suggesting a mapping, merely analogy). You have to get to know them really well to see how their personalities differ. I'm not merely talking about vaguely similar personalities, that are the closest within a limited population, but rather the nearest neighbors in personality-space across the entirety of humanity, differing by δx.