When we look at relationships of any kind that others are engaged in and we are consumed with a thought like--- "How in the name of all that is holy and sacred, can it be that THOSE two people can possibly
be friends/lovers/significant others/life partners/business partners" etc. Well, here is the answer: You (or me), as the likely judging, external observer with severely limited awareness and deep insight into the matter, most likely cannot even begin to be aware of the specific elements of the "soul contract" that exists between these two or more people. It really is as simple as that. There is likely a soul contact present between the people that you (or me), quite appropriately, in all cases, have not been made privy to. If it were important for you (or me) to have been made privy to it, we would have been.
Additionally, an ancient Chinese proverb says, "an invisible red thread connects those destined to meet, despite the time, the place, and despite the circumstances the thread can be tightened or tangle but will never be broken."