When we can't understand the science behind something in this world, we make up mythological entities that we can relate to. We personify the forces of nature that mystify us, using our boundless imaginations to comfort us and make us feel like we have some control over these things that are much bigger than we are.
Plainly it isn't an exact science, despite it being a complex interaction of micro-decisions and corresponding thought; perhaps it doesn't always work and we pass by some potential soulmates like the proverbial ships in the night, never quite connecting. Then again, perhaps the system is tenacious and continues to run like a computer program on infinite loop, so that if at first you don't meet, you are drawn back together for another try.
The situation was extraordinary. How someone like Evangeline Jenner could have wrought such a change in St. Vincent, the most worldly of men, was difficult to understand. However, Westcliff had learned that the mysteries of attraction could not always be explained through logic. Sometimes the fractures in two separate souls became the very hinges that held them together.