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I don't find the 'percentage of soul' argument convincing, but I'd agree that people who have similar backgrounds and similar life experiences tend to have more in common, which you'd assume means a more solid basis for building a strong relationship. I mean, any relationship where one person has vastly more power than the other isn't really healthy (and money is a proxy for power).
Numbers are an abstraction. They in no way fit reality.
Numbers (and mathematical operations) help us to understand the world, how stuff relates to other stuff, how stuff works, etc. The modern world and all modern technology is built on understanding derived from numbers and mathematics.