CM there is no such thing as a soulmate if that is defined as:
The one single person ever to exist who is perfect for you as a mate.
There are people you are good with, and one's you aren't. Try to find the best you can. You can only ever do your best.
Also, you seem to be harping on the following idea:
"Why don't you just give it a chance with the girl you are one night standing with? Why throw away the possibility before even trying?"
Here is why. I know you are inexperienced and all so I will lay this out for you, about how one night stands and all that actually go:
90% of these hook ups occur from contact made at a party. A large portion of these parties contain alcohol.
One or more of you will likely, then, be drunk, because having a one night stand is something you need to lower your inhibitions to be able to do.
So we will say that you and she are buzzed and you think each other are hot and you haven't had any in a while, either of you, and you hit it off, kind of, and you start dancing or something, and then you're drunk so you do one of those "why the hell not just go for it" kind of moves and make out with her.
So now you're both horny and you get led or lead her away and then you figure out where the two of you can go to make things more interesting, then you go there, then you either do or don't seal the deal, but if you do, then voila you have had a one night stand.
What happens now? There you are laying there in the laxity that is post-coitus. There she is hopefully in the same (else you have failed as a partner lol). Then you look over at her, and by now you are less drunk, and this thought comes to you:
"Shit.. who the fuck is this girl?"
But now your inhibitions are back up, she's not as hot as you thought, and you feel a little awkward and gross. You want to get the fuck out so you make something up, or if she's asleep you just kind of leave. Maybe you say I had a good time, or something, and then you're gone. You may or may not have ever asked her name.
So here's why you don't "give it a chance."
Because you can't. It isn't socially acceptable to turn to her in that moment and say: "Hey what is your name and phone number and would you like this to be a real relationship?" No. I mean, it's possible maybe if you have her contact info but it is not likely you or she will have any desire to do anything but never talk about what you did again.
Sure you might see them at a party again, and hook up again, and still never talk to them about it during the day if you see them...
The fact of the matter is that there is no assumption of compatibility in a relationship at all. That is a much more difficult and complicated set of criteria to meet than is sexual compatibility. For that you just need working organs, some experience, and a bit of stamina.
I could draw a venn diagram of it for you but the bottom line is, it's unlikely and also socially unacceptable.
See what I mean?