Please note that as there are so many replies I have not read them all, if I have repeated anyone apologies
I think that because we believe they are. It's like anything, if they are in your frame of reference and there are enough people giving energy to it, then the existence shall become real. This is so with all things.
Even our thoughts can do this, we might decide that our boss does not like us and then as time goes by this will become apparent to us because it will be all that we are looking for. We will see it everywhere.
Therefore, it does exist. Otherwise, by this maxim everything that we perceive is an illusion. Unless this is the true answer to the conundrum. It's all perception.
To this tune I just believe that they are, I believe that they are our feelings based on all the experience that we have had from birth to now. My other half thinks it's all nonsense, he does not believe in it. However, this does not stop me from feeling that there is something in our connection.
Although in truth right now once again I wonder whether these thoughts and ideas trap us with people that are no good for us.
I have not really had the time to research this, however I do believe that the twin flame/ self/ pairing etc appears in mythology of many cultures. Japan has the story of the twin pines, Joo and Uba and the idea that they will be together in all eternity. Chinese mythology has a name for twins - they call it the red string of fate I believe. I am sure that mythology covers many of the countries. The whole tf concept derives from folklore.
To my mind twins are each other and in my heart i believe that they are just that. I don't like the idea that we were split. I believe that I am whole in myself. I liken the experience to two peas in a pod. My twin was with me in my pod so to speak and therefore i feel safe when with twin. When not being triggered and in drama activation of course *falls about laughing!!*
You could say that they were your closest off world buddy and you promised that when you met in this life you'd be together. However all the glitz and glitter of this world made the promise too large and sometimes these partners don't want to honour the promise. There's too much fun out there and our promise is not Fun!!! *lol*