When you look at your own natal chart, alone, the bare positions of these traditional points, outside of their traditional astrological interpretations, mean nothing. They're just there. But overlay your parents, your siblings, your children, your co-workers, the people in your recent phone or email correspondence, your progressions, and the current positions in the sky and you'll start to see individual degree areas bunching up like crazy, in a provocative fashion. It's not random, there are regular clusters, and over a lifetime the clusters stay in the same places. Whatever the specific degrees - usually (but not always) obvious degrees in your own chart - they repeat themselves again and again. It's like you're locked into a weave that was there when you were born and keeps coming back to you, a celestial family with DNA that's totally extraterrestrial. Journalists these days bemoan the lack of family and social connections - the fact is, there are more there than you may want, you just haven't noticed it. And further, like biological family but more permanent, you're stuck with them.
Astrologers see it all the time, but rarely note it except in passing. I remember when I had an ad in the New York City yellow pages, and over ten years only people with lots of similar degrees called, no random pattern there. They could have called anybody else in the listings, but they didn't. They called me. All the others simply didn't call. They called the other astrologers in the yellow pages who had their degrees, instead. There are some degree areas (not populated in my own chart) which I have simply never met. No reason to cross paths, apparently. And other astrologers regularly report the same. Is it some cosmic principle of attraction? Paul Kammerer thought so, and it's why he believed "synchronicity" was no accident. It's a great tool for rectification (finding someone's true birthtime, when they don't know it) - all you have to do is collect charts of all their friends and family and the preponderance of the degrees that turn up are their natal angles).
It forms the essence of traditional astrological compatability, synastry, and comparison. Whatever the immediate passion between two people, if they have lots of shared degrees between their charts, they will tend to stay together, at least as friends, or even enemies. Circumstances just tend to shepherd them both into the same situations. If they have few degree contacts, even the greatest passion will have to fight circumstances just to stay in the same neighborhood. Composite charts are another story, as they start slowly, but gain momentum over time, but they, too, usually reflect the same degrees. Of course, there are many people you have never met with lots in common with you, and you don't know them, yet. But once you actually meet, just watch how difficult it becomes to escape them. That's perhaps why first meetings and introductions are so important - they are gateways to floods of experience that you may quickly lose control over.
In non-astrological terms, this type of event is considered ordinary. It's just the way life works. For all the gossip, Hollywood stars marry other Hollywood stars - mainly because that's the world they live in and they never get to meet anybody else, even if they occasionally go out and meet ordinary people elsewhere. But the same principle appears to extend to the rest of life, in ways where we don't get to go choose to meet other "ordinary" people elsewhere, because we're not even aware of the option. And if we do accidentally meet, we don't notice them, and they don't notice us, like ships passing in the night.
The mathematics and the probabilities of this could be debated forever, but the ultimate test is specific and often anecdotal. Don't you notice it yourself? Have you known anyone for very long that doesn't have a lot of degree areas in common with you? At a glance, it should become obvious. After that, you begin to focus on the individual common degrees and see which parts of that warp and weft you share with another influence each of you, one to the other. Is it Saturn (a teacher) or Jupiter (an inspirer), perhaps Mar or Venus (physical, sexual), or raw energy and timing with Sun and Moon and the Angles? But if there is no commonality, it just doesn't generally happen long enough to answer the question - the term "star-crossed" meant just that when it was coined. Some of us are swimming in the same river together, others simply aren't.
How do you explain this? Probably that mutual attraction thing. Astronomically, the planets do it, by gravitation, and it's described by LaGrange points. A simple extrapolation of these five points defines all the common astrological aspects and their meanings. It's about repetition and locking yourself into the familiar by simply doing it over and over again, just like the tides that go in and out.
Only it's more complicated, like the tides themselves. Some creatures live their lives and meet their mates only at high tide, others only at low tide, others only at certain points in between. Most are never even aware of those who do otherwise, on a different tide. Just a simple look at how we individually overlap by degree areas shows this same principle in action. Cosmically, astrologically, gravitationally, however you want to put it, it's about the greater family you are thrown into simply by your beginning, regardless of biological ties. You may not notice it right away, but as you get older you begin to just know them at first glance, although astrological awareness and comparisons really help to flush out the details - oh, here comes another one, and another one, some better, some not so nice. You can't avoid them, they're family.
The question and decision at any one moment is, "Should I invite them in?"