The first ever written reference to each person having a destined mate was given from the ancient Greek philosopher, Plato (427 BC-348 BC). Plato's theory was that each human being is part of one soul, in which they only have half of. The idea is that the soul was "split-apart" and separated from each other– and, since that time, the two halves have been forever searching for one another in order to join together and regain their sense of original created wholeness.
Many serious theorists propose that each of these alleged halves of the one soul learns all of life's lessons at their own pace, and if the two halves happen to cross paths at some point during life, they may have a powerful bond; because they are each other's "split-apart". They find a truly genuine connection, they're so alike in emotions or issues, that in some cases it's too much for them to handle.
There are many studies and theorists that support this type of idea. As well as, a few movies, such as, "The Butcher's Wife" or many other romance movies out there. Another source that I feel definitely supports the idea of "split-aparts" is the story of Adam and Eve. I'm not saying any religious preferences and opinions of my own personal life. I'm simply stating that the bible is a very important book to hundreds of thousands of people across the globe, and the story of Adam and Eve talks about them being one and being split in two. Being each other's "split-apart".
Here's where my personal, hopeless romantic self kicks in. Do I believe in a "split-apart", a "meant to be" a destiny? It's a very abstract and sometimes unappealing idea to many, but I honestly believe in the soul and a "meant to be". Each person has a "split-apart" out there, but they don't always find them. For example, the people who are forever alone. They didn't come across the other half, and decided not to settle on just any companion to keep them company. And you could object to that statement and say that it's false and that some people just chose to be alone and like to be alone, but what if they were to come across that one person, that person that is their "split-apart" would it change everything?
Now the question that rises is, when/if you meet your "split-apart" how will you know? I read an article about a man who claimed he had met his "split-apart", ten years previously to writing his article. He claimed it was "too much" for him, like Plato's theory states could occur. The way the man explained his reason for knowing it was her, was by stating that it was "an easy, natural kind of love", "a different kind of love he had ever felt." The man said he knew when he saw her, that it was something out of the ordinary; that when he looked her in the eyes, everything just made sense.
When/if one were to meet their "split-apart", I believe it should be unique, unplanned and give you a feeling that you've never felt with another. I guess it's one of those things that you are unsure about, until you look at someone and wonder, "Is this what it feels like?"